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55dc83ec884044ee93bd47fcd40b71c9db8df8e3e50c37ff6c99a3b606efe366
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2026-01-07T00:00:00-05:00
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Cosmic Collider Gravitational Waves sourced by Right-handed Neutrino production from Bubbles: Testing Seesaw, Leptogenesis and Dark Matter
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arXiv:2601.02458v1 Announce Type: new Abstract: We study a minimal type-I seesaw framework in which a first-order phase transition (FOPT), driven by a singlet scalar, produces right-handed neutrinos (RHNs) through bubble collisions, realizing a cosmic-scale collider that probes ultra-high energy scales. The resulting RHN distribution sources novel low-frequency gravitational-waves (GWs) in addition to the standard bubble-collision contribution. A stable lightest RHN can account for the observed dark matter (DM) relic abundance for masses as low as $M_{1} \equiv m_{\rm DM} \gtrsim 10^{6}\,\mathrm{GeV}$, with the associated novel GW signal accessible in LISA, ET and upcoming LVK detectors. If the RHNs are unstable, their CP-violating decays generate the observed baryon asymmetry via leptogenesis for $M_{1} \gtrsim 10^{11}\,\mathrm{GeV}$ and phase transition temperatures $T_* \gtrsim 10^{6}\,\mathrm{GeV}$, for which the novel GW spectrum is detectable in ET, BBO and upcoming LVK. If RHN decays also populate a dark-sector fermion with mass $m_{\chi} \in [10^{-4},10^{4}],\mathrm{GeV}$, successful co-genesis of baryons and asymmetric dark matter occurs for $T_* \gtrsim 10^{7}\,\mathrm{GeV}$ and $M_{1} \gtrsim 10^{9}\,\mathrm{GeV}$, naturally explaining $\Omega_{\rm DM} \simeq 5\Omega_{\rm B}$. The corresponding GW signals are testable with LISA, ET, and BBO. Finally, we analyze a UV-complete multi-Majoron model, based on a global $U(1)_N \times U(1)_{\rm B-L}$ extension, motivated from the hierarchy of lepton masses, which we dub as Mojaron collider. The corresponding FOPT in this model leaves a distinctive GW signature arising from RHN production during $U(1)_N$ symmetry breaking detectable by BBO, ET and upcoming LVK. Successful leptogenesis is realized for heaviest RHN mass $M_3 \sim 10^{10}\,\mathrm{GeV}$ and a $U(1)_N$ breaking vev $v_2 \sim \mathcal{O}(\mathrm{TeV})$, which sets the seesaw scale.
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https://arxiv.org/abs/2601.02458
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f7fd81d596ff8cbb29afb3d33f945b7bdbf5cf26c6c52ea984db7505795d24a1
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2026-01-07T00:00:00-05:00
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Neutrino flavor instabilities in neutron star mergers with moment transport: slow, fast, and collisional modes
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arXiv:2601.02461v1 Announce Type: new Abstract: Determining where, when, and how neutrino flavor oscillations must be included in large-scale simulations of hot and dense astrophysical environments is an enduring challenge that must be tackled to obtain accurate predictions. Using an angular moment-based linear stability analysis framework, we examine the different kinds of flavor instabilities that can take place in the context of the post-processing of a neutron star merger simulation, with a particular focus on the collisional flavor instability and a careful assessment of several commonly used approximations. First, neglecting anisotropies of the neutrino field, we investigate the extent to which commonly used monoenergetic growth rates reproduce the results obtained from a full multi-energy treatment. Contrary to the large discrepancies found in core-collapse supernova environments, we propose a simple combination of energy-averaged estimates that reproduces the multi-energy growth rates in our representative simulation snapshot. We then quantify the impact of additional physical effects, including nuclear many-body corrections, scattering opacities, and the inclusion of the vacuum term in the neutrino Hamiltonian. Finally, we include the neutrino distribution anisotropies, which allows us to explore, for the first time in a multi-energy setting, the interplay between collisional, fast, and slow modes in a moment-based neutron star merger simulation. We find that despite a dominance of the fast instability in most of the simulation volume, certain regions only exhibit a collisional instability, while others, especially at large distances, exhibit a slow instability that is largely underestimated if anisotropic effects are neglected.
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https://arxiv.org/abs/2601.02461
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204b70880a9f6d1fc66505737438456aa5a664246349f7b2dc08229e3e712ff0
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2026-01-07T00:00:00-05:00
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Exposure-averaged Gaussian Processes for Combining Overlapping Datasets
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arXiv:2601.02462v1 Announce Type: new Abstract: Physically motivated Gaussian process (GP) kernels for stellar variability, like the commonly used damped, driven simple harmonic oscillators that model stellar granulation and p-mode oscillations, quantify the instantaneous covariance between any two points. For kernels whose timescales are significantly longer than the typical exposure times, such GP kernels are sufficient. For time series where the exposure time is comparable to the kernel timescale, the observed signal represents an exposure-averaged version of the true underlying signal. This distinction is important in the context of recent data streams from Extreme Precision Radial Velocity (EPRV) spectrographs like fast readout stellar data of asteroseismology targets and solar data to monitor the Sun's variability during daytime observations. Current solar EPRV facilities have significantly different exposure times per-site, owing to the different design choices made. Consequently, each instrument traces different binned versions of the same "latent" signal. Here we present a GP framework that accounts for exposure times by computing integrated forms of the instantaneous kernels typically used. These functions allow one to predict the true latent oscillation signals and the exposure-binned version expected by each instrument. We extend the framework to work for instruments with significant time overlap (i.e., similar longitude) by including relative instrumental drift components that can be predicted and separated from the stellar variability components. We use Sun-as-a-star EPRV datasets as our primary example, but present these approaches in a generalized way for application to any dataset where exposure times are a relevant factor or combining instruments with significant overlap.
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https://arxiv.org/abs/2601.02462
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cd4da59b5d0636c1c4faf7ea9d925ccc58e5b77f378b0ea2d477881b1202e0dc
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2026-01-07T00:00:00-05:00
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Electron temperature relations and the direct N, O, Ne, S and Ar abundances of 49959 star-forming galaxies in DESI Data Release 2
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arXiv:2601.02463v1 Announce Type: new Abstract: We present the largest direct-method abundance catalogue of galaxies to date, containing measurements of 49$\,$959 star-forming galaxies at $z 8.105\pm0.004$ dex. We show that the S/O and Ar/O abundance ratios are strongly correlated, consistent with the expected additional Type Ia enrichment channel for S and Ar. In this work we present an initial survey of the key properties of the sample, with this dataset serving as a foundation for extensive future work on galaxy abundances at low redshift.
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https://arxiv.org/abs/2601.02463
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0e6fed6c3f4128cf295d0cc975f96dfedd3cedf83728d23c2fd885fbb5a1f98d
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2026-01-07T00:00:00-05:00
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A possible challenge for Cold and Warm Dark Matter
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arXiv:2601.02466v1 Announce Type: new Abstract: Measuring the density profile and mass concentration of dark-matter haloes is a key test of the standard cold dark matter paradigm. Such objects are dark and thus challenging to characterise, but they can be studied via gravitational lensing. Recently, a million-solar-mass object was discovered superposed on an extended and extremely thin gravitational arc. Here we report on extensive tests of various assumptions for the mass density profile and redshift of this object. We find models that best describe the data have two components: an unresolved point-mass of radius $\leq10$ pc centred on an extended mass distribution with an almost constant surface density out to a truncation radius of 139 pc. These properties do not resemble any known astronomical object. However, if the object is dark matter-dominated, its structure is incompatible with cold dark matter models, but may be compatible with a self-interacting dark matter halo where the central region has collapsed to form a black hole. This detection could thus carry substantial implications for our current understanding of dark matter.
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https://arxiv.org/abs/2601.02466
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91bfe5e52eb4d98548d82338dcc250a70d0f35b3d4efd1f2d44cabb5d3d3fd9c
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2026-01-07T00:00:00-05:00
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On the exceptionality of exceptional gravitational-wave events
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arXiv:2601.02467v1 Announce Type: new Abstract: In gravitational-wave astronomy, as in other scientific disciplines, ``exceptional'' sources attract considerable interest because they challenge our current understanding of the underlying (astro)physical processes. Crucially, ``exceptionality'' is defined only relative to the rest of the detected population. For instance, among all gravitational-wave events detected so far, GW231123 is the binary black hole with the largest total mass, while GW241110 is the binary black hole with the most strongly misaligned spin relative to the orbital angular momentum. Mandel [Astrophys.J.Lett. 996 (2026) 1, L4] argued that apparent ``exceptionality'' may reflect measurement error rather than an extreme true value, and suggested that the total mass of GW231123 may be significantly overestimated. Here we present a quantitative analysis that supports this conceptual point. We find that claims of ``exceptionality'' obtained under agnostic priors should be critically questioned whenever measurement uncertainties are comparable to the width of the underlying population. Specifically, we find that the total mass of GW231123 is unlikely to be meaningfully affected by this effect while the spin of GW241110 is far less likely to be anti-aligned than initially claimed: about 70% of realizations that appear to yield an ``exceptionally anti-aligned'' spin are in fact consistent with either nonspinning or aligned configurations.
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https://arxiv.org/abs/2601.02467
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90237fdbdd2c6afffb90dd68291abaa5ab1c10f6ff83e37312725723e5a285a2
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2026-01-07T00:00:00-05:00
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Hunting for the First Explosions at the High-Redshift Frontier
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arXiv:2601.02469v1 Announce Type: new Abstract: The James Webb Space Telescope (JWST) has spectroscopically confirmed galaxies up to $z\sim14$, 300 Myr after the Big Bang, and several candidates have been discovered at $z\sim15-25$, with one candidate as high as $z\sim30$, only 100 Myr after the Big Bang. Such objects are unexpected, since theoretical studies have not predicted the existence of detectable galaxies at $z\sim30$. While any $z\sim30$ candidates may be contaminants at lower redshifts, we explore whether such extreme redshift sources could be consistent with hyper-energetic transient events linked to the formation of the first, metal-free, stars. Specifically, we consider pair-instability supernovae (PISNe), a predicted class of extreme thermonuclear explosions that leave no remnant behind. Using cosmological simulations, we investigate an overdense cosmic region, where star formation and subsequent PISNe occur at $z\sim30-40$, even within standard cosmology. Assessing the likelihood of such a region, the corresponding number of PISNe at $z\gtrsim20$, and their observed flux, we find that JWST has a non-negligible chance to detect a PISN event at extremely high redshifts. If a transient event were confirmed at $z\sim30$, this would provide a direct glimpse into the epoch of first star formation, dramatically extending the empirical reach of astronomy.
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https://arxiv.org/abs/2601.02469
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7a1d494e09f78f847f317236a54a26be4a0b8edf49aaf88afcaf402d683bb76d
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2026-01-07T00:00:00-05:00
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The Maximum Gravity Model for partial Tidal Disruption Events: Mass Loss, Peak Fallback Rate and Dependence on Stellar Properties
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arXiv:2601.02476v1 Announce Type: new Abstract: A star entering the tidal sphere of a supermassive black hole (SMBH) can be partially stripped of mass, resulting in a partial tidal disruption event (TDE). Here we develop an analytical model for properties of these events, including the peak fallback rate, $\dot{M}_{\rm peak}$, the time at which the peak occurs, $t_{\rm peak}$, and the amount of mass removed from the star, $\Delta M$, for any star and any pericenter distance associated with the stellar orbit about the black hole. We compare the model predictions to 1276 hydrodynamical simulations of partial TDEs of main-sequence stars by a $10^6 M_\odot$ SMBH. The model yields $t_{\rm peak}$ predictions that are in good agreement (to within tens of percent) with the numerical simulations for any stellar mass and age. The agreement for $\dot{M}_{\rm peak}$ is weaker due to the influence of self-gravity on the debris stream dynamics, which remains dynamically important for partial TDEs; the agreement for $\dot{M}_{\rm peak}$ is, however, to within a factor of $\sim 2-3$ in the majority of cases considered, with larger differences for low-mass stars ($M_\star \lesssim 0.5 M_\odot$) on grazing orbits with small mass loss. We show that partial TDE lightcurves for disruptions caused by $\sim 10^6M_\odot$ SMBHs can span $\sim 20-100$ day peak timescales, whereas grazing encounters of high-mass stars with high-mass SMBHs can yield longer peak timescales ($t\gtrsim 1000$ days), associated with some observed transients. Our model provides a significant step toward an analytical prescription for TDE lightcurves and luminosity functions.
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https://arxiv.org/abs/2601.02476
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cb414de0aada576326ab4a9a2d4fea0e3babc282e7dc4e823f4196d85bd03b39
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2026-01-07T00:00:00-05:00
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Towards a global model for planet formation in layered MHD wind-driven discs: A population synthesis approach to investigate the impact of low viscosity and accretion layer thickness
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arXiv:2601.02479v1 Announce Type: new Abstract: Planet formation is inherently linked to protoplanetary disc evolution, which recent developments suggest is driven by magnetised winds rather than turbulent viscosity. We study planet formation in magnetohydrodynamic (MHD) wind-driven discs, assuming accretion occurs in a laminar surface layer above a weakly turbulent midplane. Our goal is to assess the global consequences of recent hydrodynamical results, including inefficient midplane heating and the existence of two Type II migration regimes: slow viscosity-dominated and fast wind-driven migration. We perform single-embryo planetary population syntheses with varying initial disc conditions (i.e. disc mass, size and angular momentum transport), and embryo starting locations, testing different prescriptions for the accretion layer thickness $\Sigma_\text{active}$. Thin ($\lesssim0.01\mathrm{g\,cm^{-2}}$) or fast ($\gtrsim12\%$ sonic velocity) accretion layers result in slow, viscosity-dominated regime which strongly limits the extent of Type II migration. For thick ($\gtrsim1\mathrm{g\,cm^{-2}}$) or slow ($\lesssim3\%$ sonic velocity) accretion layers, fast wind-driven Type II migration occurs frequently, leading to long-range inward migration that sets in once planets reach masses sufficient to block the accreting layer. Disk-limited gas accretion is also strongly affected by deep and early gap opening, limiting maximum giant planet masses. These effects strongly influence the final mass-distance distribution. For thin layers, giant planets form nearly in situ once they have entered Type II migration, which happens already at a few Earth masses, while thick layers lead to numerous migrated Hot Jupiters. Overall, we find that while the global properties of the emerging planet population are strongly modified relative to classical viscous discs, key properties of the observed population can be reproduced within this new paradigm.
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https://arxiv.org/abs/2601.02479
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4abe5f60ac86aefbfcc91a2e02b7bc3bd7d60a6a3e4f8fdf3d1ba6dc7bb9a942
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2026-01-07T00:00:00-05:00
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Cosmic Chance Superpositions: Largest Catalog of Quasar-Galaxy Pairs at a Projected Separation of $D \lesssim 20$ kpc
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arXiv:2601.02480v1 Announce Type: new Abstract: We present the largest catalogue to date of Galaxies On Top Of Quasars (GOTOQs), systems where the sightline to a background quasar passes directly through or very close to a foreground galaxy. Using $\approx$1.1 million quasar spectra from SDSS DR16 and the DESI Early Data Release, we identify 1345 unique GOTOQs over the redshift range $0.0045 \leq z \leq 1.09$, more than quadrupling the number previously known. The catalogue combines both absorption agnostic and absorption selected searches, enabling a statistically robust characterization of gas in galaxies at projected separations $D \lesssim 20$ kpc. The GOTOQ emission line ratios indicate that their host galaxies are predominantly normal, star forming disks with typical dust extinctions of $A_V \approx 0.5$ mag. We measure the MgII covering fraction at $D \lesssim 20$ kpc and find it to be remarkably high, $f_c = 98.2^{+1.3}_{-4.5}$ per cent, indicating that these systems trace gas rich, metal enriched regions at the disk halo interface. The median colour excess towards the quasar line of sight, $E(B-V) = 0.087$, is significantly higher than that of typical MgII absorbers, underscoring the dust rich nature of GOTOQ sightlines. From a high signal to noise composite spectrum, we report the first statistical detection of the diffuse interstellar band at $\lambda 4428$ ($W_r = 0.055 \pm 0.011$ angstrom), revealing the presence of complex organic molecules at the disk halo interface. This catalogue provides a powerful reference sample for future multi wavelength studies of gas flows, cold gas, and dust evolution in the inner circumgalactic medium.
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https://arxiv.org/abs/2601.02480
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601a0ce5dd896b1c68d71f9e29ca5e8a1591fd41a865c4f8a97cf2a97a5a1d85
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2026-01-07T00:00:00-05:00
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Resolving the Fe K$\alpha$ Doublet of the Galactic Center Molecular Cloud G0.11-0.11 with XRISM
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arXiv:2601.02482v1 Announce Type: new Abstract: Fe K$\alpha$ line emission from Galactic center molecular clouds can be produced either via fluorescence after illumination by an X-ray source or by cosmic ray ionization. Unparalleled high-resolution X-ray spectroscopy obtained by XRISM-Resolve for the galactic center molecular cloud G0.11-0.11 resolves its Fe K$\alpha$ line complex for the first time, and points to a new method for discrimination between the X-ray reflection and cosmic ray ionization models. The Fe K$\alpha$ line complex is resolved into Fe K$\alpha_1$ at $E_{1} = 6.4040 \: \rm{keV}$ and Fe K$\alpha_2$ at $E_{2}= 6.3910 \:\rm{keV}$. Both lines have non-instrumental FWHM of $\approx 3 \:\rm{eV}$, close to the predicted quantum mechanical width of the lines, suggesting scant other sources of line broadening other than instrumental and quantum effects. We measure a radial velocity of $v_{\rm{LSR}} = 50 \pm 12_{fit} \pm 14_{scale} \:\rm{km/s}$ for G0.11-0.11, achieving the same precision reached by radio observations of such clouds. The high-resolution spectrum tests for the presence of secondary Fe K$\alpha$ lines, expected as a signature of cosmic ray proton/ion ionization. The absence of the secondary lines argues against the cosmic ray ionization model for G0.11-0.11. In the preferred X-ray reflection model, if the illuminating source is Sgr A$^{\star}$, the required luminosity for an X-ray outburst about 200 years ago is $L_8 \approx 10^{38} \:\rm{erg/s}$ in an $8\:\rm{keV}$-wide band at $8\:\rm{keV}$.
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https://arxiv.org/abs/2601.02482
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1dbf23fd7b8a72a8dbf8a5f04f65244b8df0724c503073afc3874d9c68b5219d
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2026-01-07T00:00:00-05:00
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CHANG-ES XXXVI. Effects of spectral aging on radio scale heights
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arXiv:2601.02483v1 Announce Type: new Abstract: Context. Cosmic rays and magnetic fields play an important role for the formation and evolution of galaxies. Radio continuum observations allows us to study them in the haloes of edge-on galaxies. Aims. We explore the frequency dependence of the radio scale height which depends on cosmic ray transport and electron cooling. We test the influence of fundamental galaxy properties, such as star-formation rate (SFR), mass and size. Methods. We used radio continuum data of 16 edge-on galaxies from the Continuum HAloes in Nearby Galaxies - an EVLA Survey (CHANG-ES). We included maps from the LOw Frequency ARray at 144 MHz and from the Jansky Very Large Array at 3 GHz with 7" angular resolution. We extracted vertical intensity profiles within the effective radio radius and fitted beam-convolved double- exponential models to separate thin and thick discs. For the thick radio discs, we computed mean spectral indices and scale-height ratios between 144 MHz and 3 GHz. Results. We find a mean scale-height ratio of 1.26 \pm 0.16. This is much lower than what we would expect for either cosmic ray diffusion or advection if synchrotron and inverse Compton losses dominate for the electrons. There is a moderate positive correlation between the ratio and spectral index of the thick disc: galaxies with high ratios have flat radio spectra. The ratio does not depend on any other galaxy parameter. The radio spectrum of the thick disc, as indicated by the radio spectral index, steepens with total mass (strong correlation) and flattens with SFR-to-mass surface density (moderate correlation). Conclusions. Galaxies with galactic winds have flat radio continuum spectra and large scale heights at low frequencies. This shows effective transport of cosmic rays in such systems.
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https://arxiv.org/abs/2601.02483
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aa13685f473acad7f9a1eae8a3c4f62f0a55f0b94d0f8e7ec35f11fc55f2fd63
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2026-01-07T00:00:00-05:00
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Models and Observational Predictions of Dust Traps in Protoplanetary Discs
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arXiv:2601.02486v1 Announce Type: new Abstract: This manuscript investigates the impact of key dust evolution parameters on dust retention and trapping in protoplanetary discs. Using models with and without pressure bumps, combined with radiative transfer simulations, images of the dust continuum emission at (sub-)millimeter wavelengths, their fluxes and observed disc sizes are presented. For discs without pressure bumps (smooth discs), significant dust mass can only be retained over Myr timescales when dust fragmentation velocities are low (1m/s) and with viscosity values of $\alpha=10^{-3}$. For such a combination of fragmentation velocity and viscosity, the synthetic images show a bright inner emission follow by a shallow emission with potential gaps if they are present in the gas profile as well. At higher fragmentation velocities (5-10m/s), most dust is lost due to radial drift at million-year timescales unless pressure traps are present, in which case dust masses can increase by orders of magnitude and structures are observed in synthetic images. The viscosity parameter strongly shapes observable features, with low $\alpha$ producing sharper, potentially asymmetric inner wall cavities in inclined discs due to optically thick emission. High $\alpha$ favors the appearance of shoulders around the predominant rings that dust trapping produces. However, distinguishing between different fragmentation velocities observationally remains challenging. The inferred dust disc sizes from synthetic observations do not always correspond directly to dust model sizes or to the location of pressure bumps. Finally, we discuss implications for pebble fluxes and the delivery of volatiles to the inner disc. These results emphasize the strong degeneracies among dust evolution parameters and highlight the need for multi-wavelength, high-resolution observations to disentangle the processes shaping the formation of planets in protoplanetary discs.
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https://arxiv.org/abs/2601.02486
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a4f4d5ff7afe6fcd69e1e051c9b3b0c50098a7da5a19c34c8859a97e85df0ffd
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2026-01-07T00:00:00-05:00
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Thick Disks, Thin Hopes: Suppressed Capture and Merger Rates in AGN
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arXiv:2601.02487v1 Announce Type: new Abstract: Multiple models have been suggested over the years to explain the structure and support of accretion disks around supermassive black holes, from the standard thin thermal-pressure-dominated $\alpha$-disk model to more recent models that describe geometrically thicker radiation or magnetic or turbulence-dominated disks. In any case, objects embedded in the disk (e.g. compact objects, stars, gas, dust) can undergo gravitational and hydrodynamic interactions with each other leading to interesting processes such as binary interaction/capture, gravitational wave merger events, dynamical friction, accretion, gap opening, etc. It has long been argued that disks of active galactic nuclei (AGN) can enhance the rates for many of these events; however, almost all of that analysis has assumed specific thin-disk models (with aspect ratios $H/R \lesssim 0.01$). We show here that the rates for processes such as these that are mediated by gravitational cross-sections has a very strong inverse dependence on the thickness $H/R$ (scaling as steeply as $(H/R)^{-8}$), and $H/R$ can vary in the outer disk (where these processes are often invoked) by factors $\gtrsim 1000$ depending on the assumed source of pressure support in the disk. This predicts rates that can be lower by tens of orders-of-magnitude in some models, demonstrating that it is critical to account for disk parameters such as aspect ratio and different sources of disk pressure when computing any meaningful predictions for these rates. For instance, if magnetic pressure is important in the outer disk, as suggested in recent work, capture rates would be suppressed by factors $\sim 10^{10}-10^{20}$ compared to previous studies where magnetic pressure was ignored.
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https://arxiv.org/abs/2601.02487
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80f297e909c8b5e8b55875353c27e86aa07ce878829a0205357df1cb610e742c
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2026-01-07T00:00:00-05:00
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The intermediate neutron capture process. VI. Proton ingestion and i-process in rotating magnetic asymptotic giant branch stars
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arXiv:2601.02488v1 Announce Type: new Abstract: The intermediate neutron-capture process (i-process) can occur during proton ingestion events (PIEs), which may take place in the early evolutionary phases of asymptotic giant branch (AGB) stars. We investigate the impact of rotational and magnetic mixing on i-process nucleosynthesis in low-metallicity, low-mass AGB stars. We computed AGB models with [Fe/H] = $-2.5$ and $-1.7$ and initial masses of 1 and 1.5 $M_{\odot}$ using the STAREVOL code, including a network of 1160 nuclei coupled to transport equations. Rotating models incorporate a calibrated Tayler-Spruit (TS) dynamo to account for core rotation rates inferred from asteroseismic observations of solar-metallicity sub-giants and giants. Initial rotation velocities of 0, 30, and 90 km s$^{-1}$ were considered, along with varying assumptions for magnetic mixing. We find that rotation without magnetic fields strongly suppresses the i-process due to the production of primary $^{14}$N, which is subsequently converted into $^{22}$Ne $-$ a potent neutron poison during the PIE. Including magnetic fields via the TS dynamo restores the models close to their non-rotating counterparts: strong core-envelope coupling suppresses shear mixing and prevents primary $^{14}$N synthesis, yielding i-process nucleosynthesis similar to non-rotating models. We also find that rotational mixing during the AGB phase is insufficient to affect the occurrence of PIEs. Proton ingestion event-driven nucleosynthesis proceeds similarly in asteroseismic-calibrated magnetic rotating AGB stars and non-rotating stars, producing identical abundance patterns.
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https://arxiv.org/abs/2601.02488
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171141e4ecf1be59a1e30c26d819d7db348cc7dea5f9be837f2f171957a67861
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2026-01-07T00:00:00-05:00
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Dynamical Origins of Azimuthal Metallicity Variations in the Galactic Disk: Insights from Kinematic Ridges with Gaia
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arXiv:2601.02494v1 Announce Type: new Abstract: Kinematic and spectroscopic studies in the past few years have revealed coherent azimuthal metallicity variations across the Milky Way's disk that may be the result of dynamical processes associated with non-axisymmetric features of the Galaxy. At the same time, stellar kinematics from Gaia have uncovered ridge-like features in the velocity space, raising the question of whether these chemical and dynamical substructures share a common origin. Using a sample of disk stars from Gaia DR3, we find that azimuthal metallicity variations are correlated with kinematic ridges in the V_phi-R plane, suggesting a shared origin. We utilize a suite of Milky Way test-particle simulations to assess the role of transient spiral arms, the bar, and interactions with a Sagittarius-like dwarf galaxy in simultaneously shaping both chemical and kinematic substructures. Among the physical mechanisms explored, bar and spiral arm interactions are the ones that consistently reproduce both the chemo-kinematic features and alignment observed in the Gaia data. While our model of an interaction with a Sagittarius-like dwarf galaxy can also induce kinematic and metallicity substructure, the amplitude of the azimuthal metallicity variations are too weak, suggesting this is likely not the dominant influence. Although additional contributing processes cannot be ruled out, the azimuthal metallicity variations observed in Gaia are best explained by a dynamical origin. Our results support the view that that azimuthal metallicity variations in the Galaxy are driven by similar dynamical mechanisms responsible for generating the kinematic ridges and co-moving groups.
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https://arxiv.org/abs/2601.02494
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8df024b7a863ccce8b0946f4464224ba5773ecf23b01bd964f3812e0796d9a52
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2026-01-07T00:00:00-05:00
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Gas rotation and turbulence in the galaxy cluster Abell 2029
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arXiv:2601.02495v1 Announce Type: new Abstract: We constrain the rotation and turbulent support of the intracluster medium (ICM) in Abell 2029 (A2029), using dynamical equilibrium models and a combination of state-of-the-art X-ray datasets. We reduce and conduct the spectral analysis of the XRISM/Resolve data. The rotating, turbulent ICM in the model has a composite polytropic distribution in equilibrium in a spherically-symmetric, cosmologically motivated dark halo. The profile of rotation velocity and the distribution of turbulent velocity dispersion are described with flexible functional forms, consistent with the properties of synthetic clusters formed in cosmological simulations. Adopting realistic profiles for the metallicity distribution of the ICM and for the point spread function of XRISM and XMM-Newton, we tune via a Markov chain Monte Carlo algorithm the observables of the intrinsic quantities of the plasma in our model to reproduce the radial profiles of the thermodynamic quantities as derived from the spectral analysis of the XMM-Newton and Planck maps and the measurements of the line-of-sight (LOS) non-thermal velocity dispersion and redshift (probing the LOS velocity) in the XRISM pointings. Our model accurately reproduces the measurements of redshift and LOS non-thermal velocity dispersion, as further demonstrated by simulating and analyzing synthetic counterparts of the XRISM spectra, in accordance with the posterior distribution of our model. We find turbulence-to-total pressure ratio $\approx$ 2% across the (0 - 650) kpc radial range, and a rotation-to-dispersion velocity ratio peaking at 0.15 between 200 - 600 kpc. The hydrostatic-to-total mass ratio is $\approx$ 0.97 at r2500, the radius enclosing an overdensity of 2500 times the average value.
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https://arxiv.org/abs/2601.02495
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0a4b186f9817d6e1ebc8e805aec47a3ffbfe0d9c5f9afbe0d6e52ce22b5d778c
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2026-01-07T00:00:00-05:00
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Dynamically consistent analysis of Galactic WN4b stars
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arXiv:2601.02498v1 Announce Type: new Abstract: Many Wolf-Rayet (WR) stars have optically thick winds that cloak the hydrostatic layers of the underlying star. In these cases, traditional spectral analysis methods are plagued by degeneracies that make it difficult to constrain parameters such as the stellar radius and the deeper density and velocity structure of the atmosphere. Focussing on the regime of nitrogen-rich WN4-stars with strong emission lines, we employ hydrodynamically-consistent modelling using the PoWR-HD code branch to perform a next generation spectral analysis. The inherent coupling of the stellar and wind parameters enables us to break parameter degeneracies, constrain the wind structure, and get a mass estimate. With this information, we can draw evolutionary implications and test current mass-loss descriptions for WR stars. We selected a sample of six Galactic WN4b stars. Applying updated parallaxes from Gaia DR3 and calculating PoWR-HD models that sufficiently resemble most of their spectral appearance, we obtain new values for the stellar and wind parameters of the WN4b sample. We compare our results to previous studies employing grid models with a beta = 1 velocity structure and cross-check our derived parameters with stellar structure predictions from GENEC and FRANEC evolution tracks. For all six targets, we obtain a narrow range of stellar temperatures T~140 kK, in contrast to previous grid-model analyses. We confirm the existence of WRs with luminosities as low as log L/Lsol = 5.0 and M~5 Msol. All derived velocity fields include a plateau feature at ~85% of the terminal velocity. Both the distance updates and the switch to dynamically-consistent atmospheres lead to substantial parameter adjustments compared to earlier grid-based studies. A comparison of the derived mass-loss rates favours a different description for the WN4b sample than for WN2 stars analysed with the same methodology.
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https://arxiv.org/abs/2601.02498
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Academic Papers
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80a64b1b7139d94a523ba47ab6236eaccf5084f5d3160bb7170804170f283d74
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2026-01-07T00:00:00-05:00
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The origin of strong $\alpha$-element bimodalities in FIRE simulations of Milky Way-mass galaxies
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arXiv:2601.02520v1 Announce Type: new Abstract: One of the Milky Way's characteristic features is a strongly bimodal distribution of $\alpha$-process elements, such as Mg, at fixed [Fe/H] in stellar abundances. We examine patterns in [Mg/Fe] versus [Fe/H] in FIRE-2 simulations of Milky Way-mass galaxies. Out of 16 galaxies, 4 are capable of producing a strongly bimodal distribution. In all four galaxies, the high-$\alpha$ population corresponds to an older, radially-compact, thick disk, and the low-$\alpha$ population corresponds to a younger, radially-extended, thin disk, similar to the MW.The transition from high- to low-$\alpha$ took $0.3-1.2\Gyr$ and began $5.5-6.5\Gyr$ ago. [Mg/Fe] decreased at relatively fixed [Fe/H], both in the galaxy overall and at fixed radii: Fe enrichment nearly balanced gas accretion (and therefore dilution), but Mg enrichment was weaker. Importantly, this transition occurred during a period of relatively low gas fraction ($5-15\%$), immediately after a rapid decline in star formation (halving within a few hundred Myr), which caused an increase in Fe-producing white-dwarf supernovae relative to Mg-producing core-collapse supernovae. Only one case coincided with a major merger coalescence. We find similar trends in measuring stars by their current radius and by their birth radius, therefore, radial redistribution did not play a dominant role in the formation of a bimodality or its spatial dependence today. Overall, in FIRE-2, strong $\alpha$-element bimodalities are relatively uncommon ($\sim25\%$), often not associated with a major merger, and arise primarily from a rapid decline in star formation during relatively low gas fraction.
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https://arxiv.org/abs/2601.02520
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Academic Papers
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52dc77e32f5ab7b15a8975c569f72ce3bbde7389e3ea19e27fed7216d953f481
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2026-01-07T00:00:00-05:00
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Scalable Gaussian Processes for Integrated and Overlapping Measurements Via Augmented State Space Models
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arXiv:2601.02527v1 Announce Type: new Abstract: Astronomical measurements are often integrated over finite exposures, which can obscure latent variability on comparable timescales. Correctly accounting for exposure integration with Gaussian Processes (GPs) in such scenarios is essential but computationally challenging: once exposure times vary or overlap across measurements, the covariance matrix forfeits any quasiseparability, forcing O($N^2$) memory and O($N^3$) runtime costs. Linear Gaussian state space models (SSMs) are equivalent to GPs and have well-known O($N$) solutions via the Kalman filter and RTS smoother. In this work, we extend the GP-SSM equivalence to handle integrated measurements while maintaining scalability by augmenting the SSM with an integral state that resets at exposure start times and is observed at exposure end times. This construction yields exactly the same posterior as a fully integrated GP but in O($N$) time on a CPU, and is parallelizable down to O($N/T + \log T$) on a GPU with $T$ parallel workers. We present smolgp (State space Model for O(Linear/log) GPs), an open-source Python/JAX package offering drop-in compatibiltiy with tinygp while supporting both standard and exposure-aware GP modeling. As SSMs provide a framework for representing general GP kernels via their series expansion, smolgp also brings scalable performance to many commonly used covariance kernels in astronomy that lack quasiseparability, such as the quasiperiodic kernel. The substantial performance boosts at large $N$ will enable massive multi-instrument cross-comparisons where exposure overlap is ubiquitous, and unlocks the potential for analyses with more complex models and/or higher dimensional datasets.
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https://arxiv.org/abs/2601.02527
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Academic Papers
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b5879abb166dad6b9497936a9b89fa6958c7717fc86fa70891b90f317b6b38a0
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2026-01-07T00:00:00-05:00
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Catching 3I/ATLAS Using a Solar Oberth
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arXiv:2601.02533v1 Announce Type: new Abstract: The third interstellar object to be discovered, 3I/ATLAS, has a unique and continually unfolding story to tell about its nature and origin as it is monitored by telescopes on Earth, orbiting Earth and around the Solar System. Previous research into missions using chemical propulsion have only really addressed the direct case, where the opportunity to launch already expired before 3I/ATLAS's discovery. In contrast, investigations herein exploit 'Optimum Interplanetary Trajectory Software' to simulate an alternative indirect option for chemical propulsion, namely the Solar Oberth Manoeuvre (SOM). For a SOM, a low perihelion burn provides maximum benefit from the Oberth Effect, and accelerates the spacecraft rapidly towards the receding 3I/ATLAS. Though in principle feasible, results indicate this option presents significant challenges. For possible launch years between 2031 and 2037 inclusive, a 2035 launch permits the most efficient transfer to 3I/ATLAS. The reference mission requires a SOM at 3.2 Solar Radii from the Sun's centre, with an intercept after 35-50 years. It is found the SOM can leverage spacecraft masses up to $\sim{500}$ kg. Two or three solid propellant boosters could deliver the required SOM $\Delta$V, and furthermore a refuelled Starship Block 3 in LEO has sufficient performance for such a mission. As inevitable with a SOM, some of the payload mass would be needed for a heat shield to protect against the high solar flux at low perihelion.
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https://arxiv.org/abs/2601.02533
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Academic Papers
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23590e260bf95f3a5bbf57d7b9ce167595ba7d1e45034ca94bd1afff5607a2ed
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2026-01-07T00:00:00-05:00
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Composite Bulges - V. Detecting signatures of gas inflows in IFU data: The MUSE view of ionised gas kinematics in nearby galaxies
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arXiv:2601.02534v1 Announce Type: new Abstract: Using VLT/MUSE data, we study the ionised-gas kinematics in a mass- and volume-limited ($M_* \geq 10^{10} M_\odot$, $D \leq 20$\,Mpc) sample of 21 nearby galaxies to identify signatures of extended shocks within their inner kiloparsec, which appear as coherent velocity jumps in kinematic maps. By removing angular momentum, shocks in gas cause inflows, which can trigger nuclear star formation and fuel AGN activity. To identify the signatures of extended shocks, we examine residual velocity fields after subtracting a modelled rotating disc, and we study velocity difference between various gas tracers. Combining our kinematic analysis with BPT ionisation diagnostic maps and dust morphology, we find that 11 of 21 galaxies ($\sim$52%) show extended shock signatures with velocity jumps consistent with models of bar-driven shocks. This is likely a lower limit, as three additional galaxies ($\sim$15%) exhibit shocks along bars, potentially reaching the nucleus but obscured by AGN outflows. We trace shock signatures inwards close to the resolution limit, which suggests that shocks may be the prevailing mechanism of inflow in the central kpc of galaxies. The only two unbarred galaxies in our sample are also the only systems with unperturbed kinematics and no shocks, strongly linking the perturbed gas dynamics in centres of galaxies to the presence of bars. All galaxies with inner bars show LINER- or Seyfert-like nuclear emission, whereas galaxies without inner bars exhibit all emission types, indicating that regardless of gas supply, inner bars suppress star formation in galactic nuclei.
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https://arxiv.org/abs/2601.02534
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23da7132dca0f39b886218e6ca7356d86fce15a29c99c2a17973b391a06842c3
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2026-01-07T00:00:00-05:00
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Tracing Pebble Drift History in Two Protoplanetary Disks with CO Enhancement
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arXiv:2601.02545v1 Announce Type: new Abstract: Pebble drift is an important mechanism for supplying the materials needed to build planets in the inner region of protoplanetary disks. Thus, constraining pebble drift's timescales and mass flux is essential to understanding planet formation history. Current pebble drift models suggest pebble fluxes can be constrained from the enhancement of gaseous volatile abundances when icy pebbles sublimate after drifting across key snowlines. In this work, we present ALMA observations of spatially resolved $^{13}$C$^{18}$O J=2-1 line emission inside the midplane CO snowline of the HD 163296 and MWC 480 protoplanetary disks. We use radiative transfer and thermochemical models to constrain the spatial distribution of CO gas column density. We find that both disks display centrally peaked CO abundance enhancement of up to ten times of ISM abundance levels. For HD 163296 and MWC 480, the inferred enhancements require 250-350 and 480-660 Earth Masses of pebbles to have drifted across their CO snowlines, respectively. These ranges fall within cumulative pebble mass flux ranges to grow gas giants in the interior to the CO snowline. The centrally peaked CO enhancement is unexpected in current pebble drift models, which predict CO enhancement peaks at the CO snowline or is uniform inside the snowline. We propose two hypotheses to explain the centrally-peaked CO enhancement, including a large CO desorption distance and CO trapped in water ice. By testing both hypotheses with the 1D gas and dust evolution code chemcomp, we find that volatile trapping (about 30\%) best reproduces the centrally peaked CO enhancement observed.
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https://arxiv.org/abs/2601.02545
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caa1de19222fe77a7c99c2326eb05663524e046c5abe2a81217ee776ca5c7251
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2026-01-07T00:00:00-05:00
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Dearth of Photosynthetically Active Radiation Suggests No Complex Life on Late M-Star Exoplanets
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arXiv:2601.02548v1 Announce Type: new Abstract: The rise of oxygen in the Earth's atmosphere during the Great Oxidation Event (GOE) occurred about 2.3 billion years ago. There is considerably greater uncertainty for the origin of oxygenic photosynthesis, but it likely occurred significantly earlier, perhaps by 700 million years. Assuming this time lag is proportional to the rate of oxygen generation, we can estimate how long it would take for a GOE-like event to occur on a hypothetical Earth-analog planet orbiting the star TRAPPIST-1 (a late M star with Teff 2560 K). Although in the habitable zone, an Earth-analog planet located in TRAPPIST-1e's orbit would receive only 0.9% of the Photosynthetically Active Radiation (PAR) that the Earth gets from the Sun. This is because most of the star's light is emitted at wavelengths longer than the 400-700 nm PAR range. Thus it would take 63 Gyrs for a GOE to occur. But the linear assumption is problematic; as light levels increase, photosynthesis saturates then declines, an effect known as photoinhibition. Photoinhibition varies from species to species and depends on a host of environmental factors. There is also sensitivity to the upper wavelength limit of the PAR: extending just 50 nm increases the number of photons by a factor of 2.5. Including these and other factors greatly reduces the timescale to roughly 1-5 Gyrs for a GOE. However, non-oxygenic photosynthetic bacteria can thrive in low-light environments and can use near-IR light out to 1100 nm, providing 22 times as many photons. With this huge light advantage, and because they evolved earlier, anoxygenic photosynthesizers would likely dominate the ecosystem. On a late M-star Earth-analog planet, oxygen may never reach significant levels in the atmosphere and a GOE may never occur, let alone a Cambrian Explosion. Thus complex animal life is unlikely.
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https://arxiv.org/abs/2601.02548
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Academic Papers
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6cfca533255e0e6295b2aaf8962c85a894249cfc7b02a5253e7ae60c4dfba1d7
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2026-01-07T00:00:00-05:00
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Using 23 Years of ACS/SBC Data to Understand Backgrounds: Significant Reductions in Expected Background Levels
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arXiv:2601.02551v1 Announce Type: new Abstract: We have used 23 years of Hubble Space Telescope ACS/SBC data to study what background levels are encountered in practice and how much they vary. The backgrounds vary considerably, with F115LP, F122M, F125LP, PR110L, and PR130L all showing over an order of magnitude of variation in background between observations, apparently due to changes in airglow. The F150LP and F165LP filters, which are dominated by dark rate, not airglow, exhibit a far smaller variation in backgrounds. For the filters where the background is generally dominated by airglow, the backgrounds measured from the data are significantly lower than what the ETC predicts (as of ETC v33.2). The ETC predictions for `average' airglow are greater than the median of our measured background values by factors of 2.51, 2.64, 105, and 3.64, for F115LP, F122M, F125LP, and F140LP, respectively. A preliminary analysis suggests this could be due to certain OI airglow lines usually being fainter than expected by the ETC. With reduced reduced background levels, the shorter-wavelength SBC filters can conduct background-limited observations much more rapidly than had previously been expected. As of ETC v34.1, a new option will be included for SBC calculations, allowing users to employ empirical background percentiles to estimate required exposure times.
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https://arxiv.org/abs/2601.02551
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Academic Papers
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a160e711daa4556429a199538ea08d298bc69e9a8a85056a0883f07ef8fc2bd6
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2026-01-07T00:00:00-05:00
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The Lazuli Space Observatory: Architecture & Capabilities
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arXiv:2601.02556v1 Announce Type: new Abstract: The Lazuli Space Observatory is a 3-meter aperture astronomical facility designed for rapid-response observations and precision astrophysics across visible to near-infrared wavelengths (400-1700 nm bandpass). An off-axis, freeform telescope delivers diffraction-limited image quality (Strehl $>$0.8 at 633 nm) to three instruments across a wide, flat focal plane. The three instruments provide complementary capabilities: a Wide-field Context Camera (WCC) delivers multi-band imaging over a 35' $\times$ 12' footprint with high-cadence photometry; an Integral Field Spectrograph (IFS) provides continuous 400-1700 nm spectroscopy at R $\sim$ 100-500 for stable spectrophotometry; and an ExtraSolar Coronagraph (ESC) enables high-contrast imaging expected to reach raw contrasts of $10^{-8}$ and post-processed contrasts approaching $10^{-9}$. Operating from a 3:1 lunar-resonant orbit, Lazuli will respond to targets of opportunity in under four hours--a programmatic requirement designed to enable routine temporal responsiveness that is unprecedented for a space telescope of this size. Lazuli's technical capabilities are shaped around three broad science areas: (1) time-domain and multi-messenger astronomy, (2) stars and planets, and (3) cosmology. These capabilities enable a potent mix of science spanning gravitational wave counterpart characterization, fast-evolving transients, Type Ia supernova cosmology, high-contrast exoplanet imaging, and spectroscopy of exoplanet atmospheres. While these areas guide the observatory design, Lazuli is conceived as a general-purpose facility capable of supporting a wide range of astrophysical investigations, with open time for the global community. We describe the observatory architecture and capabilities in the preliminary design phase, with science operations anticipated following a rapid development cycle from concept to launch.
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https://arxiv.org/abs/2601.02556
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cb4a601f6b20a6ed9a8f455eaad328b4aa908274de13fa4fc3f81fa1df99db76
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2026-01-07T00:00:00-05:00
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COUGS-DESI: A Catalog of Unusual Galaxies with Polar Structures in the DESI Legacy Imaging Surveys
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arXiv:2601.02579v1 Announce Type: new Abstract: Polar-structure galaxies (PSGs) host photometrically and kinematically decoupled components oriented at large angles to one another. These systems, which include polar rings, polar disks, polar halos, polar bulges, polar dust lanes, and polar tidal structures, provide valuable insights into galaxy formation and evolution, although their rarity has limited statistical studies. We aim to construct the largest and most homogeneous catalog of PSGs to date in order to enable robust statistical studies of their properties and occurrence rates in the local Universe. Using DESI Legacy Imaging Surveys (DR10) data, we identified PSG candidates in the Siena Galaxy Atlas (SGA) through visual inspection, convolutional neural network classification, and cross-matching with previously reported systems. Each galaxy was assigned a PSG subtype and host morphology. We analyzed general properties of PSGs and compared them with those for all galaxies in the SGA. Simple image simulations were used to evaluate projection effects. The resulting Catalog of Unusual Galaxies with polar Structures in the DESI Legacy Imaging Surveys (COUGS-DESI) contains 2,989 PSG candidates, including 342 previously known objects. Projection effects from random galaxy overlaps are negligible. The sample spans a wide range of polar morphologies, with 1,113 polar rings, 75 polar bulges, 216 polar halos, 185 polar dust lanes, and 1,315 polar tidal structures. PSGs constitute 2.2% of local non-dwarf galaxies, with polar rings representing 0.7%. Approximately 1% of S0 galaxies in the SGA host polar rings, whereas spirals constitute the most common morphological type among the PSG hosts in our catalog. COUGS--DESI increases the number of known PSG candidates by an order of magnitude and provides a foundation for detailed studies of the formation and evolution of polar structures.
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https://arxiv.org/abs/2601.02579
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7af3902570b1061508892cc57b72497531efd88284d01db89d4cfe7c654e72db
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2026-01-07T00:00:00-05:00
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Isotopic Ratios in the Disk of HD 163296
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arXiv:2601.02593v1 Announce Type: new Abstract: Isotopic abundance ratios in protoplanetary disks are critical for understanding volatile inheritance and chemical evolution in planet-forming environments. We present Atacama Large Millimeter/submillimeter Array observations of the rare isotopologue 13C18O(2-1) at approximately 0.3 arcsec resolution from the disk around the Herbig Ae star HD 163296, combined with archival observations of C17O(2-1), C18O(1-0), and C17O(1-0), to empirically constrain carbon and oxygen isotopic ratios without detailed disk modeling. Both the C17O/13C18O(2-1) and C18O/C17O(1-0) flux ratios rise sharply across the CO snowline and flatten beyond 1.5 arcsec (r >= 150 au), where the emission becomes optically thin. This transition, reflecting a steep drop in CO column density set by the disk's thermal structure, makes HD 163296 an optimal case for isotopic analysis. Using beam-averaged intensities of the four transitions measured in this optically thin region, we derive isotopic ratios of 12C/13C = 75.3 (+14.7/-11.4) and 18O/17O = 3.28 (+0.31/-0.26), both consistent with local interstellar medium values. The 16O/18O ratio remains weakly constrained due to moderate optical depth in the C18O(1-0) line and degeneracy with CO column density. These results demonstrate that rare CO isotopologues can provide robust, empirical constraints on isotopic ratios in disks when sharp structural transitions allow for the identification of optically thin regions, and establish HD 163296 as a benchmark for extending such studies to other systems with resolved snowline structures.
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https://arxiv.org/abs/2601.02593
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4310682fa07ac4ca379497f414315d4aca07f2bcfd8b5c5b47e4828b627e45b5
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2026-01-07T00:00:00-05:00
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Meteor observations as a tool to constrain cosmogonic models of the Solar System
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arXiv:2601.02599v1 Announce Type: new Abstract: Recent observations of small bodies of the Solar System showed evidence of the presence of refractory (asteroidal) material in the Oort cloud. Different models of the origin of the Solar System predict different numbers of rocky objects in the Oort cloud, meaning that measurement of this population can be used as an observational constraint for cosmogonic models. The aim of our work is to study how the data obtained from meteor observations can be used as a tool for distinguishing among the existing cosmogonic models. We investigated two meteor databases collected by the cameras of the All-Sky Meteor Orbit System (AMOS) located in the Canary Islands and in Chile. We describe methodology and results of the search for unusually strong rocky meteoroids on cometary orbits with the origin in the Oort cloud. These data will be used to calculate the fluxes of meteors of different compositions in order to constrain the ratio of icy and rocky components of the Oort cloud. For the flux determination, we estimate the observational time and effective area of the AMOS system.
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https://arxiv.org/abs/2601.02599
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e0a6952b508f221d1a05c8e33590fb88bea19576059368df0dd0d4848e29b092
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2026-01-07T00:00:00-05:00
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Exploring Composition Mixing in Kilonova Ejecta with Ray-by-ray Simulations
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arXiv:2601.02600v1 Announce Type: new Abstract: Binary neutron star merger (BNSM) ejecta are considered a primary repository of $r$-process nucleosynthesis and a source of the observed heavy-element abundances. We implement composition mixing into ray-by-ray radiation-hydrodynamic simulations of BNSM ejecta, coupled with an online nuclear network (NN). We model mixing via a gradient-based mixing approximation that evolves simultaneously with the hydrodynamics. We find that mixing occurs in regions where the electron fraction changes rapidly. While mixing smooths composition gradients in transition regions, it has a negligible impact on the heavy-element yields. This is because the primary $r$-process site (the equatorial ejecta) is initially homogeneous in free neutrons, leaving no strong gradients for mixing to act upon. In each angular ray, the abundances of the most produced elements are robust under mixing, while the less abundant ones are more affected. The total global abundances change only slightly from mixing, since each angular ray contributes its most abundant elements. Furthermore, the predicted kilonova light curves show only minor reddening, with differences below the detectability of state-of-the-art telescopes. In general, we do not observe significant effects from mixing in the time span of the $r$-process. Consequently, mixing only leads to minor variations in abundances and light curves in ray-by-ray simulations.
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https://arxiv.org/abs/2601.02600
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Academic Papers
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7b87798bc3852ccca5aff5b0c782cd01d609a4ea171103d58dbacbe7187074f0
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2026-01-07T00:00:00-05:00
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Where does the simplified Stellar Contamination Model fail in Exoplanet Transmission Spectroscopy?
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arXiv:2601.02621v1 Announce Type: new Abstract: Stellar photospheric heterogeneities (e.g., starspots, faculae) distort the stellar spectrum in transit and imprint wavelength-dependent biases on the planet-to-star radius ratio (Transit Light Source Effect, TLSE). The Rackham-TLSE (R-TLSE) prescription applies a disc-averaged correction based solely on filling factor and spectral contrast, but transmission spectroscopy also depends on limb darkening, active-region distribution, and transit geometry. We include these in a pixel-resolved framework, ECLIPSE-Xlambda, and run idealised noise-free model-model comparisons to R-TLSE. For LHS 1140 b, K2-18 b, and WASP-69 b, disc-averaged corrections differ from the pixel model by up to about 400 ppm in the optical for active hosts and non-equatorial transits, but stay below about 10 ppm in the near-infrared where limb darkening is weak. We then apply both approaches to the JWST/NIRISS SOSS spectrum of LHS 1140 b. With limb darkening set to zero, ECLIPSE-Xlambda recovers stellar-contamination parameters matching the reference R-TLSE solution, confirming consistency in the disc-averaged limit. With wavelength-dependent limb darkening, reproducing the short-wavelength slope via stellar contamination alone requires hot faculae (delta Tfac about 600 K; ffac about 0.35), equivalent to a circular facular region of radius about 0.6 Rstar (about 60% of the stellar radius) on the disc; such an extended unocculted region is physically unlikely even for an active M dwarf. Purely stellar contamination would therefore require extreme faculae, whereas a genuine atmospheric contribution complementing a more modest facular signal is more plausible. These results delineate the validity regime of R-TLSE and underscore the need for geometry-aware stellar-heterogeneity models including limb darkening in high-precision transmission spectroscopy.
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https://arxiv.org/abs/2601.02621
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8e198cc85b4bdcc1289117e779c10e50d030f7c1f20dc9f7a9fb4fd0ff094ec1
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2026-01-07T00:00:00-05:00
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E-XQR-30: Evidence for an Increase in the Ionization State of Metal Absorbers from z~6 to z~2
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arXiv:2601.02634v1 Announce Type: new Abstract: We investigate the evolution of the ionization state of metal-enriched gas in and around galaxies near the epoch of reionization using a sample of 488 metal absorption systems at 4.3<6.3 from the E-XQR-30 survey. We classify the absorption systems based on whether they display only low-ionization absorption (CII, SiII, MgII), only high-ionization absorption (CIV, SiIV), or both. The percentage of low-ionization-only systems decreases from 24% at $z\sim$6 to 2% at $z\sim$4.3, whilst the fraction of high-ionization-only systems increases from 52% to 82%. For mixed absorbers (with both low and high ionization absorption), we use the column density ratios log(N_CII/N_CIV) and log(N_SiII/N_SiIV) to quantify the average ionization as a function of redshift. The log(N_SiII/N_SiIV) ratio does not change significantly over 5$\lesssim z \lesssim$6.3. We combine the E-XQR-30 log(N_CII/N_CIV) measurements with literature measurements at $z\sim$2-4 and find that the log(N_CII/N_CIV) ratio declines by a factor of $\sim$20 between $z\sim$6 and $z\sim$2. To explore possible drivers of this evolution, we run photoionization models of gas slabs illuminated by a uniform UV background at fixed density, metallicity and HI column density. We find that the increase in the ionization state of metal absorbers towards lower redshifts can likely be explained by some combination of 1) an increase in the metallicity of CIV-absorbing gas and 2) a decrease in the typical HI column densities of the absorbing gas, driven by the declining cosmic mean density and a rapid rise in the strength of the UV background during the final stages of reionization.
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https://arxiv.org/abs/2601.02634
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77eb844ecd1b171af1722d4119f0e8f1d25307ef7158ae339748ea4c689cfd42
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2026-01-07T00:00:00-05:00
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Quantifying the Contamination of TESS Ecliptic-Plane Light Curves by Minor Planets
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arXiv:2601.02637v1 Announce Type: new Abstract: Though missions devoted to time series photometry focus primarily on targets far beyond the solar system, their observations can be contaminated by foreground minor planets, especially near the ecliptic plane where solar system objects are most prevalent. Crucially, depending on one's choice of data reduction/background estimation algorithm, these objects can induce both apparent brightening and/or dimming events in processed light curves. To quantify the impact of these objects on archived TESS light curves, we used N-body integrations of all currently known minor planets to postdict all 600,000+ of their interactions with stars selected for high-cadence observations during TESS ecliptic plane sectors. We then created mock images of these moving sources and performed simple aperture photometry using the same target and background apertures used in SPOC processing. Our resulting 10,000+ target-specific light curves, which faithfully model the time-dependent positions and magnitudes of the actual solar system objects that approached each target, reveal that $>95\%$ of high-cadence ecliptic plane targets experience a minor planet crossing within 1 TESS pixel of the source. Additionally, 50% of all $T>13$ mag targets experience at least one instantaneous moment where the contaminating flux from minor planets exceeds 1% of the target flux. We discuss these population-level results and others, and highlight several case studies of bright flybys.
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https://arxiv.org/abs/2601.02637
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beec937e0f21098ae92b35488c63fc002aacc02a7c160c6419d7689d0d7da4b5
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2026-01-07T00:00:00-05:00
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SN 2024abfl: A Flat-Plateau, Low-Luminosity Type IIP Supernova with Early CSM Interaction
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arXiv:2601.02638v1 Announce Type: new Abstract: We present photometric and spectroscopic observations of SN 2024abfl, a low-luminosity Type IIP supernova (LLSN) discovered shortly after explosion. The transient reached a peak absolute magnitude of $M_V = -14.9$ and exhibited an extended, flat plateau lasting $\sim$125 days. From the late-time bolometric light curve, we estimate a $^{56}$Ni mass of $\sim0.01~M_\odot$, consistent with other LLSNe. Analytical shock-cooling models fail to reproduce the rapid early rise, indicating that circumstellar material (CSM) interaction contributed to the initial emission. The spectroscopic evolution is typical of LLSNe, with relatively narrow metal lines and low expansion velocities ($\lesssim 3000$ km s$^{-1}$) that decline slowly over time. We detect a broad ``ledge'' feature around 4600 \AA within three days of explosion, which we interpret as a blend of high-ionization shock-accelerated CSM lines. Multi-peaked H$\alpha$ profiles develop during the plateau phase, consistent with complex ejecta-CSM interactions. As one of the best-observed examples of LLSNe, SN 2024abfl exhibits a weak explosion and signatures of nearby CSM, offering new insights into progenitor properties, pre-explosion mass loss, and the diversity of LLSNe.
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https://arxiv.org/abs/2601.02638
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6b802db8fe327987c08fc68c3bdb40898696c08e78c92ab6af3c326c19a78f93
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2026-01-07T00:00:00-05:00
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TOI-4495: A Pair of Aligned, Near-Resonant Sub-Neptunes that Likely Experienced Overstable Migration
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arXiv:2601.02665v1 Announce Type: new Abstract: We report the discovery of a sub-Neptune and a Neptune-like planet ($R_b = 2.48^{+0.14}_{-0.10}\,R_\oplus$, $R_c = 4.03^{+0.23}_{-0.15}\,R_\oplus$) orbiting the F-type star TOI-4495. The planets have orbital periods of 2.567 days and 5.185 days, lying close to a 2:1 mean-motion resonance (MMR). Our photodynamical analysis of the TESS light curves constrains the planetary masses to $M_b = 7.7 \pm 1.4\,M_\oplus$ and $M_c = 23.2 \pm 4.7\,M_\oplus$. The measured masses and radii indicate the presence of volatile-rich gaseous envelopes on both planets. The Rossiter-McLaughlin effect and the Doppler shadow of TOI-4495 c reveal a well-aligned orbit with a projected stellar obliquity of $\lambda = -2.3^{+8.3}_{-7.8}\,\mathrm{deg}$. Combined with the low mutual inclination constrained by the photodynamical analysis ($\Delta I < 8.7\,\mathrm{deg}$), the planetary orbits are likely coplanar and aligned with the host star's spin axis. We show that the planets are near, but not in, the 2:1 MMR, with a circulating resonant angle. We also find substantial free eccentricity for the inner planet, TOI-4495 b ($e_b = 0.078^{+0.020}_{-0.013}$). Given the observed proximity to the 2:1 resonance and the more massive outer planet, TOI-4495 b and c are particularly susceptible to resonant overstability, which can convert resonantly excited eccentricity into free eccentricity. However, additional mechanisms (e.g., planetesimal scattering) may be required to further excite the eccentricity by $\sim 4\%$. To prevent tidal damping from reducing the eccentricity below the observed level over the star's lifetime (1.9 Gyr), the reduced tidal quality factor of TOI-4495 b must be $Q' \gtrsim 10^5$, consistent with the presence of a thick envelope on the planet.
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https://arxiv.org/abs/2601.02665
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a413347612dde18ecd5ba9d969ebf8dc8a8e72c2c3f07847e7d9351c18b672b1
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2026-01-07T00:00:00-05:00
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The Origin of Spin-Alignment of Dark Matter Subhalos
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arXiv:2601.02678v1 Announce Type: new Abstract: Subhalo spin is essential for modeling galaxy formation and controlling systematic uncertainties in intrinsic alignment (IA) studies. However, the physical mechanisms governing subhalo spin acquisition within the tidal environments of host halos remain poorly understood. In this work, we investigate the alignment between subhalo and host halo spins using the high-resolution cosmological $N$-body simulation, Shin-Uchuu. We find that the spin alignment between subhalos and host halos becomes increasingly pronounced toward the central regions. Our analysis reveals that subhalos typically acquire spin in the same direction as their orbital angular momentum. Since the orbital angular momentum of most subhalos is aligned with the host halo spin, an overall alignment between subhalo and host spins emerges. When classified by orbital orientation, however, subhalo spins in the inner regions are found to be oriented perpendicularly or anti-parallel to the host spin for polar and retrograde orbits, respectively. These results provide strong evidence that subhalo spins are acquired through torques exerted by the tidal field of the host halo. Furthermore, we demonstrate that the mass ratio and the radial distance from the host center are the primary parameters governing subhalo spin alignment, while the dependence on the accretion redshift is found to be negligible.
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https://arxiv.org/abs/2601.02678
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e3d26d3da999409ed5fda4f9ca5f39218f851143a0abdc17dcecb32c0b7f8794
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2026-01-07T00:00:00-05:00
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The Study of a Cosmic Ray Candidate Detected by the Askaryan Radio Array
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arXiv:2601.02718v1 Announce Type: new Abstract: Experiments designed to detect ultra-high energy (UHE) neutrinos using radio techniques are also capable of detecting the radio signals from cosmic-ray (CR) induced air showers. These CR signals are important both as a background and as a tool for calibrating the detector. The Askaryan Radio Array (ARA), a radio detector array, is designed to detect UHE neutrinos. The array currently comprises five independent stations, each instrumented with antennas deployed at depths of up to 200 meters within the ice at the South Pole. In this study, we focus on a candidate event recorded by ARA Station 2 (A2) that shows features consistent with a downward-going CR-induced air shower. This includes distinctive double-pulse signals in multiple channels, interpreted as geomagnetic and Askaryan radio emissions arriving at the antennas in sequence. To investigate this event, we use detailed simulations that combine a modern ice-impacting CR shower simulation framework, FAERIE, with a realistic detector simulation package, AraSim. We will present results for an optimization of the event topology, identified through simulated CR showers, comparing the vertex reconstruction of both the geomagnetic and Askaryan signals of the event, as well as the observed time delays between the two signals in each antenna.
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https://arxiv.org/abs/2601.02718
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0d1a23e770ed0f69fc41fc96dab1bb2c634ac5888a4213303bad5232138ef57e
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2026-01-07T00:00:00-05:00
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A Tale of Two Dust Disks in Our Milky
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arXiv:2601.02724v1 Announce Type: new Abstract: Cosmic dust plays a vital role in stellar and galactic formation and evolution, but its three-dimensional structure in the Milky Way has remained unclear due to insufficient precise reddening and distance measurements. Although early studies typically adopted a single-disk model, we detect two distinct components at Galactocentric distances of 5-14 kpc, enabled by photometric, spectroscopic, and astrometric measurements of over 5 million stars. The thin dust disk's scale height increases radially from 60 to 200 pc, while the thick disk grows from 300 to 800 pc. For the first time, we find the thin and thick dust disk correlates spatially with molecular and atomic hydrogen disk, respectively. The thin, thick, and combined disks have scale lengths of 9.6+1.2-1.1 kpc, 4.2+0.4-0.3 kpc, and 6.6+0.3-0.3 kpc, respectively. The gas-to-dust ratio shows an exponential radial gradient, increasing from around 60 at 5 kpc to around 470 at 14 kpc. These findings provide new insights into dust morphology in the Galaxy and raise fundamental questions that require further investigation.
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https://arxiv.org/abs/2601.02724
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b9d101a95fded8a63de29cd582244121f1d0e2ba661e5a808cf929378c3c805e
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2026-01-07T00:00:00-05:00
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Super-Orbital Variations in Magnetar Rotation Measure Arising from the Precession of Companion Star: Implications for FRB 20220529
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arXiv:2601.02734v1 Announce Type: new Abstract: Recent observations of FRB 20220529 reveal significant variation and a partial reversal in its rotation measure (RM), suggesting the presence of a dynamically evolving magnetized environment, which could be caused by the orbital motion of the magnetar within the binary system. Here we develop the binary model by suggesting that the spin and magnetic axis of the companion star could undergo precession around the orbital axis. It is then investigated how the precession period and the inclination of the magnetic axis, as well as a possible disc wind, can influence the evolution behaviors of the RM and dispersion measure (DM) of FRB emission. As the foremost consequence, the RM variation can be significantly altered on timescales longer than the orbital period, producing super-orbital evolution and complex patterns. Applying this model to FRB 20220529, we find that its RM evolution could be reproduced with a precession period of 182 days and an inclination angle of approximately $19^{\circ}$, while the other binary parameters are fixed at their typical values. Meanwhile, the absence of significant variation of the DM argues against the presence of a dense equatorial disc around the companion star, which would be constrained by future long-term observations.
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https://arxiv.org/abs/2601.02734
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406b6c1d5b15eb08e310ea064ce6e8d8aadfb9839dbc35aaaa276b461cd2093d
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2026-01-07T00:00:00-05:00
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A Galactic Supernova Remnant Candidate at l =25.8, b=+0.2 Revealed by Near-Infrared Imaging and Spectroscopy
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arXiv:2601.02761v1 Announce Type: new Abstract: We present high-resolution near-infrared spectroscopic observations of the newly identified supernova remnant (SNR) candidate G25.8+0.2 obtained with the Immersion Grating Infrared Spectrograph (IGRINS) on the Harlan J. Smith Telescope. The source was originally discovered in the UKIRT Wide-field Infrared Survey for Fe+ (UWIFE; Lee et al. 2014). Our spectra reveal multiple kinematic components in the [Fe II] 1.644 um emission. The high-velocity components exhibit elevated [Fe II]/Br gamma ratios characteristic of shock excitation, while the low-velocity components are dominated by hydrogen and helium recombination lines and are consistent with photoionized gas, indicating an H II-region origin. G25.8+0.2 lies within the G26 complex, a large (~15'x 30', corresponding to ~28 pc x 57 pc at a distance of 6.5 kpc) star-forming region in the inner Galaxy. The shock-excited [Fe II] filaments closely trace the morphology of the bright radio shell that partially encloses centrally filled soft X-ray emission, strongly suggesting recent supernova activity in this region. We discuss the physical nature of G25.8+0.2 and its relationship to the surrounding G26 star-forming complex. In addition, we derive the extinction toward the source using Brackett-line ratios and constrain the spectral types of the dominant ionizing stars from the He I 2.058 um/Br gamma line ratios.
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https://arxiv.org/abs/2601.02761
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94cb13c35dd642507976b76bc8f81a98acb8fbe207b065ed7b0de90bbfaa4dbe
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2026-01-07T00:00:00-05:00
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Finite Plasma Beta Three-dimensional Magnetic Field Extrapolation Based on MHD Relaxation Method
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arXiv:2601.02772v1 Announce Type: new Abstract: Three-dimensional (3D) magnetic field in the solar atmosphere provides crucial information to understand the explosive phenomenon such as solar flares and coronal mass ejections. Since it is still hard that we determine the 3D magnetic field from direct observation, a nonlinear force-free field (NLFFF) extrapolation is one of the best modeling methods that provides 3D magnetic field. However, the method is based on zero-beta assumption, i.e., the model ignores the gas pressure gradient and gravitational force. The magnetic field based on an NLFFF is not well reconstructed in high-beta region, such as in chromospheric or lower height layer and in weak field region. To overcome this problem, we need to consider the magnetohydrostatic equilibrium. In this study, we developed a finite plasma beta magnetic field extrapolation method based on magnetohydrodynamic relaxation method. In our method, we consider a force balance of the Lorentz force and the gas pressure. We tested three different schemes and extrapolated 3D magnetic field using an observational photospheric vector magnetic field of one solar active region, which is a quadrupole complex sunspot group and well studied with an NLFFF. The verification of three schemes is performed by comparing the residual force, and we concluded that our methods reduce ~4% of residual force of the previous NLFFF. We also examined the plasma beta profile along the height and found that, in the core of the active region, plasma beta reaches a local minimum of ~0.01 in the lower corona with beta ~1 at the photosphere.
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https://arxiv.org/abs/2601.02772
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77a310a832c2e29594951dfd29dc2c624161794bacf8fa9e93c19d79b6b88924
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2026-01-07T00:00:00-05:00
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Indications of a Late-Time Transition to a Strongly Interacting Dark Sector
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arXiv:2601.02789v1 Announce Type: new Abstract: We explore the transition from the $\Lambda$CDM to an interacting dark sector by introducing a model with a redshift threshold that controls the onset of the energy transfer between the dark energy and the dark matter. Below the transition redshift, the interaction between dark matter and dark energy becomes active, while at earlier times the cosmological evolution coincides with that of $\Lambda$CDM. This approach allows us to determine the epoch in the comic history where the interacting effects have an impact in the description of the dark sector. We constrain the free parameters of the model using late-time cosmological observations, namely Cosmic Chronometers, DESI DR2 Baryonic Acoustic Oscillations, and Supernova data from the Pantheon Plus, Union3.0, and DES-Dovekie catalogues. The analysis provides an indication of a strong interacting term that describes energy transfer from dark energy to dark matter, which is activated at low redshifts. The PantheonPlus sample provides a threshold of $z_{T}<0.624$, the Union3.0 sample yields $z_{T}=0.400_{-0.23}^{+0.021}$, and the DES-Dovekie sample gives $z_{T}=0.371_{-0.26}^{+0.028}$. The model fits the data in a similar way to the CPL parametrization, without the dark energy to cross the phantom divide line.
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https://arxiv.org/abs/2601.02789
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fc1a94b9e71baafb3de0af0298b0e735d7227b7eadcb87d8634e36f926b33ed1
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2026-01-07T00:00:00-05:00
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A New Collision Avoidance Fiber Assignment Algorithm for Robotic Fiber Positioners in Multi-Object Spectroscopy
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arXiv:2601.02795v1 Announce Type: new Abstract: We present a new fiber assignment algorithm for a robotic fiber positioner system in multi-object spectroscopy. Modern fiber positioner systems typically have overlapping patrol regions, resulting in the number of observable targets being highly dependent on the fiber assignment scheme. To maximize observable targets without fiber collisions, the algorithm proceeds in three steps. First, it assigns the maximum number of targets for a given field of view without considering any collisions between fiber positioners. Then, the fibers in collision are grouped, and the algorithm finds the optimal solution resolving the collision problem within each group. We compare the results from this new algorithm with those from a simple algorithm that assigns targets in descending order of their rank by considering collisions. As a result, we could increase the overall completeness of target assignments by 10% with this new algorithm in comparison with the case using the simple algorithm in a field with 150 fibers. Our new algorithm is designed for the All-sky SPECtroscopic survey of nearby galaxies (A-SPEC) based on the K-SPEC spectrograph system, but can also be applied to similar fiber-based systems with heavily overlapping fiber positioners.
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https://arxiv.org/abs/2601.02795
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512da468f3892d9b87f0e6f11e12fcbb93669c6ad3ef928aff128ff1c2c67658
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2026-01-07T00:00:00-05:00
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Transient Large-Scale Anisotropy in TeV Cosmic Rays due to an Interplanetary Coronal Mass Ejection
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arXiv:2601.02801v1 Announce Type: new Abstract: Large- or medium-scale cosmic ray anisotropy at TeV energies has not previously been confirmed to vary with time. Transient anisotropy changes have been observed below 150 GeV, especially near the passage of an interplanetary shock and coronal mass ejection containing a magnetic flux rope ejected by a solar storm, which can trigger a geomagnetic storm with practical consequences. In such events, cosmic rays provide remote sensing of the magnetic field properties. Here we report the observation of transient large-scale anisotropy in TeV cosmic ray ions using data from the Large High Altitude Air Shower Observatory (LHAASO). We analyze hourly skymaps of the transient cosmic ray intensity excess or deficit, the gradient of which indicates the direction and magnitude of transient large-scale anisotropy across the field of view. We observe enhanced anisotropy above typical hourly fluctuations with $>$5$\sigma$ significance during some hours of November 4, 2021, in separate data sets for four primary cosmic ray energy ranges of median energy from $E$=0.7 to 3.1 TeV. The gradient varies with energy as $E^{\gamma}$, where $\gamma\approx-0.5$. At a median energy $\leq$1.0 TeV, this gradient corresponds to a dipole anisotropy of at least 1\%, or possibly a weaker anisotropy of higher order. This new type of observation opens the opportunity to study interplanetary magnetic structures using air shower arrays around the world, complementing existing in situ and remote measurements of plasma properties.
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https://arxiv.org/abs/2601.02801
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1b27f7f408e658c2d77e0b6fe36005ff9bce2d6871997e3237a16cbbac4c261a
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2026-01-07T00:00:00-05:00
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Beyond Sgr A* and M87*: Sub-Microarcsecond Black Hole Shadow Detection via Lunar-based Extremely Long Baseline Interferometry
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arXiv:2601.02812v1 Announce Type: new Abstract: The 1.3 mm ground-based very long baseline interferometry (VLBI) array, the Event Horizon Telescope (EHT), is limited by the Earth's diameter and can image the supermassive black hole (SMBH) shadows of only M87* and Sgr A*. Extending the array with an assumed lunar-based telescope could achieve $\sim 0.85\ \mu$as angular resolution at 230 GHz, enabling black hole shadow detection for a larger SMBH sample. The concept is motivated by space VLBI missions and lunar exploration, including the ongoing Lunar Orbit VLBI Experiment (LOVEX) aboard QueQiao-2 (Chang'E-7) and the planned International Lunar Research Station (ILRS). We assess shadow detectability for 31 SMBH with predicted large angular sizes, exploring different telescope location and antenna size. Assuming a telescope at the lunar antipode, we simulate the Moon-Earth (u,v) coverage and show that source geometry relative to the Moon's orbit determines whether the primary indicator of shadow, first visibility null, can be sampled. Using a geometric ring model, we identify six high-priority targets: M104, NGC 524, PGC 049940, NGC 5077, NGC 5252, and NGC 1052. Shadows of M104, NGC 5077, and NGC 1052 are detectable with a 5 m lunar-based telescope; PGC 049940 requires 20 m; NGC 524 and NGC 5252 require 100 m. Photon ring detection for Sgr A*, M87*, NGC 1600, and M31 is possible if space telescopes fill the baseline coverage gaps and sensitivity requirements are met. These results provide a clear scientific and technical motivation for lunar-based telescopes in future black hole shadow studies.
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https://arxiv.org/abs/2601.02812
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8b59abdf9a73bf9a6aa1bf195bde513d2751bb5c1c802485a1c9afec18e79908
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2026-01-07T00:00:00-05:00
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Nonlinear Weak Lensing reconstruction for Galaxy Clusters
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arXiv:2601.02816v1 Announce Type: new Abstract: We present a numerical investigation of nonlinear cluster lens reconstruction using weak lensing mass mapping. Recent advances in imaging and shear estimation have pushed reliable reduced shear measurements closer to cluster cores, making mass reconstruction accessible in the nonlinear regime. However, the Kaiser-Squires based algorithm becomes unstable in cluster cores, where convergence $\kappa$ significantly deviates from zero and the linear approximation breaks down. To address this limitation, we develop a reconstruction framework with two key modifications: applying smooth masks to these regions and using a model-derived analytical solution as the initial guess, rather than assuming $\kappa = 0$. We validate our framework using simulated cluster lensing data with known mass distributions, incorporating realistic masks that arise from limitations in reduced shear measurements. We show that in the absence of shape noise, our framework yields high-fidelity mass reconstruction in regions of large reduced shear, with the best-performing method achieving residuals below $0.02 \sigma$ in the unmasked regions. This pushes mass reconstruction to higher accuracy in the nonlinear regime.
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https://arxiv.org/abs/2601.02816
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71a8952bd61e1f3f27485843b5365a21eb6fe400a00c458ee3d4055d5a93f22f
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2026-01-07T00:00:00-05:00
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Studying the surface effect in Procyon A as an F-type star
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arXiv:2601.02840v1 Announce Type: new Abstract: Procyon A is an F-type main-sequence star in a binary system. It has been the subject of numerous ground-based and space-based observing campaigns, providing precise classical constraints, including a well-determined mass. It was also among the first stars in which individual frequencies were detected, making it a crucial benchmark for F-type stars. Our goal is to investigate the surface effect, namely the discrepancy between observed and model oscillation frequencies due to inadequate modeling of the surface stellar layers, especially important in F-type stars. Using Procyon A as a case study, we aim to understand how different surface correction prescriptions impact the inference of the fundamental properties of this star, and compare the results with those obtained when the surface corrections are neglected. We inferred the fundamental stellar properties employing a grid of models computed with MESA, including gravitational settling, radiative accelerations, and turbulent mixing. We selected the best-fit models using the AIMS code taking into account different methods to fit the individual frequencies. We find that the use of surface corrections can introduce uncertainties up to 7\% in the inferred stellar mass. We identify that the most reliable stellar mass estimates are obtained when using frequency ratios, the Sonoi et al. (2015) surface correction or directly fitting the individual frequencies. Our results indicate that the surface effects in F-type stars differ from those found in the Sun and in solar-like stars, highlighting the need to be careful when considering the surface corrections for these stars.
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https://arxiv.org/abs/2601.02840
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18b8ccb37e0be313bff10e00e722139afdad5a221ff1c13d01f17be396df2e60
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2026-01-07T00:00:00-05:00
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Investigating the Anisotropy of Dispersion Measure Contribution from the Galactic Halo by Using Fast Radio Bursts
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arXiv:2601.02849v1 Announce Type: new Abstract: We propose a data-driven approach to reconstruct the all-sky distribution of the dispersion measure contribution from the Galactic halo ($\mathrm{DM_{halo}}$) through a spherical harmonic expansion, enabling an investigation of its possible anisotropies. Based on the NE2001 model and using 92 localized and 574 unlocalized non-repeating fast radio bursts (FRBs) at Galactic latitudes $|b|>15^\circ$, we find a significant dipole anisotropy in $\mathrm{DM_{halo}}$, pointing toward $(l=130^\circ,\, b=+5^\circ)$ with a $1\sigma$ uncertainty of approximately $28^\circ$. The $\mathrm{DM_{halo}}$ value in this direction is $63\pm9~\mathrm{pc~cm^{-3}}$, exceeding the all-sky mean by about $2.6\sigma$. This result is not significantly affected by the choice of Galactic ISM models. Furthermore, even when using a refined sample of 62 localized FRBs (excluding CHIME detections, repeaters, and unlocalized events), the dipole anisotropic structure persists, with a direction of $(l=141^\circ,\, b=+51^\circ)$ and a larger 1$\sigma$ uncertainty of $\sim 44^\circ$. Model comparisons using the Akaike Information Criterion and Bayesian evidence yield consistent preferences, and together they suggest that current FRB data slightly favor the existence of a dipole structure in $\mathrm{DM_{halo}}$. If this feature is not a statistical fluctuation or systematic error, its physical origin requires further investigation. Future FRB samples with larger sizes and more complete sky coverage will be essential to confirm or refute this possible anisotropic structure.
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https://arxiv.org/abs/2601.02849
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68fe30b4e82e5f4c001316faf49a845a5b8cc4762361f2775a98ddaaee987021
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2026-01-07T00:00:00-05:00
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BEACON: JWST NIRCam Pure-parallel Imaging Survey. II. Physical Properties of $z=7-14$ Galaxies
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arXiv:2601.02861v1 Announce Type: new Abstract: We present photometric properties of 161 galaxy candidates at $z=7-14$ selected from the second data release (DR2) of BEACON, a JWST Cycle 2 pure-parallel NIRCam imaging program. Carefully selected from 36 independent pointings (corresponding to $\sim350$\,arcmin$^2$ sky coverage), and hence with reduced cosmic variance, our galaxy candidates provide an unbiased sample for investigating galaxy properties over a wide range of environments. We measure the physical properties, including UV continuum slope ($\beta_{\rm UV}$), stellar mass ($M_*$), star formation rate (SFR), and sizes. Our highest redshift galaxy candidate at $z=13.71\pm0.15$ has a remarkably bright UV luminosity of $M_{\rm UV}=-21.19\pm0.08$, making it the brightest galaxy at $z>12$ if spectroscopically confirmed. With an extremely blue UV slope, compact morphology, and high star formation rate surface density ($\Sigma_{\rm SFR}$), this candidate may have extremely low metallicity, high ionizing photon escape fraction, or contributions from an AGN. Among our multiple independent sightlines, we identify three fields of galaxy number overdensity with $>3\sigma$ significance. The properties of galaxies in various environments do not exhibit significant differences, implying either that accelerated galaxy evolution in overdense regions is not yet widespread at $z>7$, or that the current constraints are limited by sample size. Our simulations indicate that increasing the sample by an order of magnitude would allow such environmental trends to be robustly confirmed or ruled out, underscoring the importance of future pure-parallel observations.
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https://arxiv.org/abs/2601.02861
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78f8c527bb8e2ee0e2215b7c66fa36dca56f5db81755608b2fe85ce2412f3ec7
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2026-01-07T00:00:00-05:00
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GATOS XI : Excess dust heating in the Narrow Line Regions of nearby AGN revealed with JWST/MIRI
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arXiv:2601.02865v1 Announce Type: new Abstract: We present JWST/MIRI imaging of eight nearby Active Galactic Nuclei (AGN) from the GATOS survey to investigate the physical conditions of extended dust in their narrow line regions (NLRs). In four galaxies (ESO 428-G14, NGC 4388, NGC 3081, and NGC 5728), we detect spatially resolved dust structures extending ~100-200 pc along the NLR. In these systems, we find a strong link between the morphology of the dust, the radio ejecta, and the coronal [Si VI] emission, implying that dust carries imprints of the processes shaping the NLR. Using spatially resolved spectral energy distributions, we show that dust in the NLR has systematically steeper slopes than star forming clumps. This dust emits at temperatures in the range 150 - 220 K, at a distance of ~150 pc from the nucleus. Using simple models, we show that, even under optimistic assumptions of grain size and AGN luminosity, the excess MIR emission cannot be explained by AGN illumination alone. We interpret this excess heating as in-situ. We show that shocks with velocities of $v_{\rm shock} \sim 200- 400 \, \rm km/s$ in dense gas can close this gap, and in some cases even account for the total observed emission. This, combined with multiple lines of evidence for shocks in these regions, supports a scenario in which shocks not only coexist with dust but may be playing a key role in heating it. Our findings reveal shocks may be an important and previously overlooked driver of extended dust emission in the central hundreds of parsecs in AGN.
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https://arxiv.org/abs/2601.02865
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422d346ab41c5a120c96ee0a46b8bd61eaa6c93dd9036370e5e4b8c2b38364fc
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2026-01-07T00:00:00-05:00
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Measuring the homogeneity scale using the peculiar velocity field
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arXiv:2601.02886v1 Announce Type: new Abstract: We propose an innovative definition of the scale at which the Universe becomes homogeneous based on measurements of velocities rather than densities. When using the matter density field, one has to choose an arbitrary scale (e.g. within 1\% of the average density) to define the transition to homogeneity. Furthermore, the resulting homogeneity scale is strongly degenerate with the galaxy bias. By contrast, peculiar velocities (PV) allow us to define an unambiguous scale of homogeneity, namely the distance at which the velocities between pairs of galaxies change from being on-average correlated to anti-correlated. Physically, this relates to when the motion of pairs of galaxies is influenced by the matter density between them, rather than beyond. The disadvantage is that peculiar velocities are more difficult to measure than positions, resulting in smaller samples with larger uncertainties. Nevertheless, we illustrate the potential of this approach using the peculiar velocity correlation functions obtained from the Sloan Digital Sky Survey PV catalog, finding an homogeneity scale of $R_H\approx 133\substack{+28 \\ -52}\, \rm{Mpc/h}$. Finally, we show that more precise measurements are within reach of upcoming peculiar velocity surveys, and highlight this homogeneity scale's potential use as a standard ruler within the standard cosmological model.
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https://arxiv.org/abs/2601.02886
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9439a528e110d5a953bfb1d9f807a7bb85c4ebd489f07afd5347f7359ace5fe2
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2026-01-07T00:00:00-05:00
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Probing ionized bubbles around luminous sources during reionization with SKA 21-cm observations
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arXiv:2601.02889v1 Announce Type: new Abstract: Detecting and characterizing individual ionized bubbles during the Epoch of Reionization (EoR) using the redshifted HI 21-cm signal provides a direct probe of the early ionizing sources and the intergalactic medium. We develop and validate a computationally efficient estimator that operates on gridded visibilities to detect ionized bubbles. This serves as an accurate alternative to the more computationally demanding bare estimator that uses all baselines and frequency channels. Further, we employ a non-parametric foreground-subtraction method based on Gaussian process regression, which minimizes loss of the HI 21-cm signal and yields improved signal-to-noise ratios. Our analysis indicates that ionized bubbles at redshifts $z \sim 7 - 8$ can be detected with SNR $\gtrsim 10$ using $\sim 100$ hours of SKA1-Low AA$^*$ and AA4 observations. We further derive a scaling relation that connects the SNR to the bubble radius, redshift, total observing time, and the mean neutral hydrogen fraction of the surrounding IGM. This helps to quickly predict the observational outcome for any planned observations and is, therefore, useful for devising observational strategies. Finally, we apply a Bayesian likelihood framework with Markov Chain Monte Carlo sampling to the residual visibilities to recover ionized bubble properties, including radius, position, and the mean neutral fraction. The resulting posterior distributions demonstrate accurate recovery of the bubble parameters. This confirms the feasibility of robustly characterizing individual ionized regions with the SKA1-Low.
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https://arxiv.org/abs/2601.02889
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7320043edc0753aa0bcdd1bb30ce0bd3c820e4108e393289dfccd014fc80649b
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2026-01-07T00:00:00-05:00
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Asteroseismology of solar-like oscillators: emulating individual mode frequencies with a branching neural network
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arXiv:2601.02926v1 Announce Type: new Abstract: Accurately measuring stellar ages and internal structures is challenging, but the inclusion of asteroseismic observables can substantially improve precision. However, the curse of dimensionality means this comes at a high computational cost when using standard interpolation methods across grids of stellar models. Furthermore, without a rigorous treatment of random uncertainties in grid-based modelling, it is not possible to address systematic errors in stellar models. We present PITCHFORK -- a multilayer perceptron neural network with a branching architecture capable of rapid emulation of both classical stellar observables and individual asteroseismic oscillation modes of solar-like oscillators. PITCHFORK can predict the classical observables $T_{\text{eff}}$, $L$, and $\left[\mathrm{Fe}/\mathrm{H}\right]$ with precisions of $5.88\,\text{K}$, $0.014\,\text{L}_{\odot}$, and $0.001\,\text{dex}$, respectively, and can predict 35 individual radial mode frequencies with a uniform precision of $0.02$ per cent. PITCHFORK is coupled to a vectorised Bayesian inference pipeline to return well-sampled and fully marginalised posterior distributions. We validate our rigorous treatment of the random uncertainties -- including the asteroseismic surface effect -- in an extensive hare-and-hounds exercise. We also demonstrate our ability to infer the stellar properties of benchmark stars -- namely, the Sun and the binary stars 16 Cygni A and B. This work demonstrates a computationally scalable and statistically robust framework for stellar parameter inference of solar-like oscillators using individual asteroseismic mode frequencies. This provides a foundation for the treatment of systematics in preparation for the imminent abundance of asteroseismic data from future missions.
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https://arxiv.org/abs/2601.02926
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b0f9b92ec4230e14152dc37965c4f12cd03b5f7448a296024e6d1a6a125076ed
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2026-01-07T00:00:00-05:00
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Discovery of an Extremely Luminous Type II Cepheid in the Andromeda Giant Stellar Stream: Evidence for a Hierarchical Triple with an Inner Binary Merger
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arXiv:2601.02960v1 Announce Type: new Abstract: We report the discovery of LAMOST J0041+3948, the most luminous post-AGB Type II Cepheid (TIIC) known, located in the Andromeda Giant Stellar Stream. Its spectral energy distribution (SED) exhibits a strong near-infrared excess, indicating the presence of a circumbinary dusty disk and hence binarity. SED fitting yields an effective temperature of $T_{\rm eff}=6738_{-262}^{+234}\,$K and a post-AGB luminosity of $\log(L/L_{\odot})=4.32_{-0.08}^{+0.07}$. Comparison with theoretical evolutionary tracks suggests a ~$2.0$-$4.0\,M_{\odot}$ progenitor when accounting for a possible scattered-light contribution. ZTF Light curves reveal a pulsation period of 89d that lies close to the period-luminosity relation for long-period RV Tauri stars. Follow-up spectroscopy reveals clear $s$-process enrichment and signatures consistent with an accretion disk around the companion. The inferred progenitor is significantly younger and more massive than a typical stream member, suggesting that an additional mechanism such as a stellar merger is required. We propose a formation channel in which the present post-AGB binary descends from a hierarchical triple system. In this scenario, the inner binary merged after the system was displaced to its current location by the galaxy merger event, and the resulting massive merger remnant subsequently evolved into the extremely luminous post-AGB star observed today.
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https://arxiv.org/abs/2601.02960
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c102aad63990633dcd22da9ba630b2d25136a77c699e892abd2c0d436353b342
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2026-01-07T00:00:00-05:00
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Polarization of the CMB in the Standard Model Extension
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arXiv:2601.02961v1 Announce Type: new Abstract: In standard cosmology, Cosmic Microwave Background photons near the last scattering surface exhibit only linear polarization due to Compton scattering, leading to the assumption that primordial circular polarization is negligible. However, the physics of Lorentz violation (LV), associated with specific operators, can influence these polarization characteristics. This study employs the Boltzmann equation within the framework of the Standard Model Extension (SME) to explore how the background LV tensor $ K_{AF} $ can induce circular polarization in CMB radiation. By computing the transformation of linear polarization into circular polarization and utilizing the Faraday conversion angle, we derive a bound for $ K_{AF} $ on the order of $ 10^{-41} \, \text{GeV} $, aligning with recent findings. Additionally, we consider the total pure photon terms within the SME, demonstrating that LV in the presence of scalar perturbations can also generate cosmic birefringence (CB) in the CMB radiation. Through analysis of best-fitting CB angles, we establish a more stringent bound of approximately $ 10^{-32} \, \text{GeV} $ for $ K_{F} $.
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https://arxiv.org/abs/2601.02961
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463391130804d9cf42fb6114f27209a7989e7d43649a87cf383905185ebbcd4b
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2026-01-07T00:00:00-05:00
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Mean opacity tables for probing the interior and atmosphere of giant planets
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arXiv:2601.02995v1 Announce Type: new Abstract: We present new Rosseland and Planck mean opacity tables relevant to the shallow interiors and atmospheres of giant planets. The tables span metallicities from 0.31 to 50 times solar, temperatures from 100 - 6000 K, and pressures from 1e-6 - 1e5 bar, thereby covering a wider parameter space than previous data sets. Our calculations employ the latest molecular and atomic line lists and pressure-broadening treatments, and include contributions from collision-induced absorption, free electrons, and scattering processes. We further provide cloudy mean opacity tables that account for cloud particle extinction across a range of particle sizes and capture the sequential removal of condensates as the gas cools. We benchmark our cloud-free tables against widely used opacity tables and find significant relative differences, exceeding 100% in Rosseland mean opacities at T \gtrsim 3000 K due to the inclusion of additional short-wavelength absorbers. Differences in Planck mean opacities at high temperatures are even larger, in some cases exceeding two orders of magnitude, which is most likely driven by the inclusion of Ca, Mg, and Fe cross-sections and updated Na D and K I resonance line treatments. Cloud opacities substantially increase Rosseland mean opacities for T \lesssim 2800 K, while their effect on Planck mean opacities is weaker. We also discuss limitations of our mean opacities at high pressures, where non-ideal effects become important. This work provides improved cloud-free mean opacity tables for giant planets, as well as the first publicly available cloudy mean opacity tables, which will enable more realistic modeling of their atmospheres and interiors.
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https://arxiv.org/abs/2601.02995
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6274114b8ddb1b4a4291f18299690988a8e7e5281317f65726868515de6e77cf
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2026-01-07T00:00:00-05:00
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Bounce Inflation with Dynamical Dark Energy in Light of DESI DR2
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arXiv:2601.03028v1 Announce Type: new Abstract: Recently, the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2) suggests that the dark energy in our universe might be evolving, favoring the Chevallier-Polarski-Linder (CPL) parameterization and a lower Hubble constant. In our previous work, it has been reported that cosmological model with the non-singular bounce inflation (BI) scenario and $\Lambda$CDM might alleviate the Hubble tension into 3$\sigma$ confidence. In this paper, we study the cosmological model of BI with a dynamical dark energy. We find that individual consideration of the CPL parameterization and the data \texttt{DESI DR2} tend to larger Hubble constants for both BI and power law (PL) case with cosmic microwave background (CMB) data. Employing BI with combined CPL parameterization and \texttt{DESI DR2}, we obtain the Hubble constant $H_ 0 = 65.2^{ + 1.8}_{ - 2.2} \ \mathrm{km} \cdot \mathrm{s}^{ -1 } \cdot \mathrm{Mpc}^{ -1 }$, which is larger than $H_ 0 = 64.0 \pm 2.1 \ \mathrm{km} \cdot \mathrm{s}^{ -1 } \cdot \mathrm{Mpc}^{ -1 }$ for the PL case. After considering nontrivial weak lensing effect and spatial curvature as well as adding \texttt{Pantheon+}, BI fits 3.1$\sigma$ confidence of $\Lambda$CDM with $w_ 0 = -0.919 \pm 0.038$ and $w_{ \mathrm{a}} = -0.37 \pm 0.12$, and it prefers evolving dark energy than the PL case with $w_ 0 = -0.960 \pm 0.074$ and $w_{ \mathrm{a}} = -0.15^{ +0.28}_{ -0.25}$.
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https://arxiv.org/abs/2601.03028
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69442ce6dbe6e4fab9f8bd904fd721c593ff5098595f54f934a333a7d86adda8
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2026-01-07T00:00:00-05:00
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The winds of OBA hypergiants and luminous blue variables: Dynamically-consistent atmosphere models reveal multiple wind regimes
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arXiv:2601.03072v1 Announce Type: new Abstract: OBA hypergiants (OBAHGs) are evolved massive stars with notable wind features in their optical spectrum. Positioned at the cool edge of the line-driven wind regime, many are candidate luminous blue variables (LBVs) likely near the Eddington Limit. Although brief, this evolutionary stage deeply impacts their surroundings and subsequent evolution. We study the mechanisms behind OBAHG winds and spectra, covering the temperature range of non-eruptive LBVs. Using the PoWR atmosphere code, we compute models with an Eddington parameter Gamma_e ~ 0.4 and moderate turbulent pressure, typical for cool hypergiants, varying the effective temperature from ~12.5 to ~38.0 kK at solar metallicity. Our models show a complex temperature-dependent mass-loss pattern, with regions of higher/lower rates linked to two wind solutions: "dense" and "airy." Spectra of known OBAHGs and LBVs match models from all solution regions. We find bi-stability jumps -- with sharp mass-loss increases -- at temperatures where Fe IV recombines to Fe III (and Fe III to Fe II). "Drops" in mass-loss also occur when the leading Fe ion changes at wind onset, signaling a switch to airy solutions under insufficient driving opacity. The resulting velocity fields also reflect these different regimes: airy solutions match the empirical terminal velocity vs temperature relation, while dense ones deviate. Turbulent pressure is crucial for wind acceleration at cooler temperatures, especially in airy regimes. We demonstrate that the bi-stability jumps exist in OBAHGs but are part of a broader complex behavior not replicated by current mass-loss recipes. Combining our and other recent results, we suggest that the switch between airy and dense solutions only occurs within a certain proximity to the Eddington Limit. Testing this requires future models with broader parameters and advanced treatments of radiatively-driven turbulence.
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https://arxiv.org/abs/2601.03072
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e29abeed73afbda17aeff3e80280586c72dd1900eb916e35259754b3b7d75e9d
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2026-01-07T00:00:00-05:00
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A Long Tidal Feature Extending from a Low-Redshift Galaxy Revealed in Rubin Data Preview 1 Imaging
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arXiv:2601.03080v1 Announce Type: new Abstract: Using the Vera C. Rubin Observatory Data Preview 1 (DP1), we present the detection and photometric analysis of a stellar stream extending along the minor axis of a massive disk-galaxy, LEDA 751050, at a redshift of z = 0.1 in the Extended Chandra Deep Field-South (ECDFS). This feature appears to be an analog of the M31 Giant Stellar Stream, spanning around 130 kpc by 15 kpc, with an estimated stellar mass of M_* = 6x10^8 M_Sun, and a mean g-band surface brightness (SB) of mu_g = 28.6 mag/arcsec^2. This discovery demonstrates Rubin's ability to reveal low-SB substructures and foreshadows the future capabilities when the full Legacy Survey of Space and Time (LSST) data set is actualized.
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https://arxiv.org/abs/2601.03080
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fa4f7b61c95a8d80b3c09632054684a7bf4c485fb4a6554cca5f523c9c8014d5
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2026-01-07T00:00:00-05:00
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Late-time Background Constraints on Linear and Non-linear Interacting Dark Energy after DESI DR2
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arXiv:2601.03122v1 Announce Type: new Abstract: In this study, we present observational constraints on a class of phenomenological interacting dark energy (IDE) models that admit analytical solutions for the Hubble parameter $H(z)$. We consider a set of five linear and three non-linear IDE scenarios, encompassing both interactions proportional to the dark matter and/or dark energy densities, as well as non-linear combinations of the two. For all eight IDE models, we find a better fit than $\Lambda$CDM from a $\Delta\chi^2$ analysis for both combinations of datasets considered. When using the Akaike Information Criterion ($\Delta$AIC), we find a similarly improved fit in all cases, except for one dataset combination in $Q=3H\delta\rho_{\rm de}$. Our analysis also shows a preference for sign-switching interactions, with energy transfer from dark energy to dark matter at low redshift, reversing direction at higher redshift. These results should be interpreted with caution, as the latter direction of energy transfer is accompanied by negative dark energy densities in the past, which may be unphysical. Models that do not allow sign-changing behaviour instead show a preference for energy flow from dark matter to dark energy, and hence negative dark energy densities. The only exceptions are $Q=3H\delta\rho_{\rm de}$ and $Q=3H\delta\left(\tfrac{\rho_{\rm de}^2}{\rho_{\rm dm}+\rho_{\rm de}}\right)$, which exhibit energy flow in the opposite direction. Furthermore, for all interactions considered, we find a phantom-divide crossing in the effective dark energy equation of state $w^{\rm eff}_{\rm de}$, with the dark energy density decreasing ($w^{\rm eff}_{\rm de}>-1$) at present and at low redshift, while increasing ($w^{\rm eff}_{\rm de}<-1$) in the past at high redshift. These results highlight the promising, but problematic, nature of dark sector interactions, as well as the need to extend the analysis using early-time physics and datasets.
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https://arxiv.org/abs/2601.03122
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be39b2f5032dfd475ef3dc7093fa363331eb474c855784e9be1db0208894d65a
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2026-01-07T00:00:00-05:00
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Large-scale radio bubbles around the black hole transient V4641 Sgr
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arXiv:2601.03140v1 Announce Type: new Abstract: Black holes (BHs) in microquasars can launch powerful relativistic jets that have the capacity to travel up to several parsecs from the compact object and interact with the interstellar medium. Recently, the detection of large-scale very-high-energy (VHE) gamma-ray emission around the black hole transient V4641 Sgr and other BH-jet systems suggested that jets from microquasars may play an important role in the production of galactic cosmic rays. V4641 Sgr is known for its superluminal radio jet discovered in 1999, but no radio counterpart of a large-scale jet has been observed. The goal of this work is to search for a radio counterpart of the extended VHE source. We observed V4641 Sgr with the MeerKAT radio telescope at the L and UHF bands and produced deep maps of the field using high dynamic range techniques. We report the discovery of a large-scale (35 pc), bow-tie-shaped, diffuse, radio structure around V4641 Sgr, with similar angular size to the extended X-ray emission discovered by XRISM. However, it is not spatially coincident with the extended VHE emission. After discussing the association of the structure with V4641 Sgr, we investigate the nature of the emission mechanism. We suggest that the bow-tie structure arose from the long-term action of large-scale jets or disk winds from V4641 Sgr. If the emission mechanism is of synchrotron origin, the radio/X-ray extended structure implies acceleration of electrons up to more than 100 TeV as far as tens of parsecs from the black hole.
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https://arxiv.org/abs/2601.03140
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21f28b2d5b808df5891e045a451cbea6fcc33677bb80143473b026c4ea548bfe
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2026-01-07T00:00:00-05:00
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Helioseismic Evidence That the Solar Dynamo Originates near the Tachocline
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arXiv:2601.03238v1 Announce Type: new Abstract: The exact location of the solar dynamo remains uncertain--whether it operates primarily in the near-surface shear layer, throughout the entire convection zone, or near the tachocline, a region of sharp transition in the solar rotation, located at the base of the convection zone, approximately 200,000 km beneath the surface. Various studies have supported each of these possibilities. Notably, the solar magnetic "butterfly" diagram and the pattern of zonal flows ("torsional oscillations") exhibit strikingly similar characteristics, suggesting a link between magnetic field evolution and solar flows. Since magnetic fields cannot be measured directly in the deep solar interior, torsional oscillations and rotation gradients are employed as diagnostic proxies. Our analysis reveals that the gradient of rotation displays "butterfly"-like behavior near the tachocline, which is similar to the magnetic butterfly diagram at the surface. This result supports the idea that the solar dynamo has a deep-seated origin, likely operating either near the tachocline or throughout the convection zone, thereby disfavoring the recent scenario of a shallow, near-surface dynamo. This finding may also have important implications for understanding how stellar dynamos operate in general.
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https://arxiv.org/abs/2601.03238
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8e80e1cf76899f478cc849877f48c7c2b48b5ef22894fd5d7450b6034abe5d72
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2026-01-07T00:00:00-05:00
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The Squeezed Bispectrum from CHIME HI Emission and Planck CMB Lensing: Current Sensitivity and Forecasts
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arXiv:2601.03240v1 Announce Type: new Abstract: Line intensity mapping using atomic hydrogen (HI) has the potential to efficiently map large volumes of the universe if the signal can be successfully separated from overwhelmingly bright radio foreground emission. This motivates cross-correlations, to ascertain the cosmological nature of measured HI fluctuations, and to study their connections with galaxies and the underlying matter density field. However, these same foregrounds render the cross-correlation with projected fields such as the lensing of the cosmic microwave background (CMB) difficult. Indeed, the correlated Fourier modes vary slowly along the line of sight, and are thus most contaminated by the smooth-spectrum radio continuum foregrounds. In this paper, we implement a method that avoids this issue by attempting to measure the non-linear gravitational coupling of the small-scale 21cm power from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with large-scale Planck CMB lensing. This measurement is a position-dependent power spectrum, i.e. a squeezed integrated bispectrum. Using 94 nights of CHIME data between $1.0 < z < 1.3$ and aggressive foreground filtering, we find that the expected signal is five times smaller than the current noise. We forecast that incorporating the additional nights of CHIME data already collected would enable a signal-to-noise ratio of 3, without any further improvements in filtering for foreground cleaning.
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https://arxiv.org/abs/2601.03240
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35636502baad594f540ac10f5c250303ae219e860e96e546f329dcf8554a6c1d
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2026-01-07T00:00:00-05:00
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Heavy Black-Holes Also Matter in Standard Siren Cosmology
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arXiv:2601.03257v1 Announce Type: new Abstract: With the release of the Gravitational-Wave Transient Catalog GWTC-4.0 by the LIGO-Virgo-KAGRA (LVK) collaboration, 218 candidate detections of gravitational waves (GWs) from compact binary coalescences (CBCs) have been reported. This milestone represents a major advancement for GW cosmology, as many methods, particularly those employing the spectral siren approach, critically depend on the number of available sources. We investigate the impact of a novel parametric model describing the full population mass spectrum of CBCs on the estimation of the Hubble constant. This model is designed to test the impact of heavy black holes in GW cosmology. We perform a joint inference of cosmological and population parameters using 142 CBCs from GWTC-4.0 with a false alarm rate smaller than 0.25 per year, using both spectral and dark siren approaches. With spectral sirens, we estimate the Hubble constant to be $H_0 = 78.8^{+19.0}_{-15.3}\,{\rm km s^{-1} Mpc^{-1}}$ (68% CL), while the dark siren method yields $H_0 = 82.5^{+16.8}_{-14.3}\,{\rm km s^{-1} Mpc^{-1}}$ (68% CL). These results improve the uncertainty by approximately 30.4% and 36.2%, respectively. We show that this improvement is linked to the presence of a new mass scale in the binary black hole mass spectrum at $63.3^{+4.8}_{-4.8}\,M_{\odot}$, which provides additional constraints on the Hubble constant. Besides providing the tightest standard-siren constraints on $H_0$, this highlights the importance of a heavy-mass feature in the black hole spectrum.
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https://arxiv.org/abs/2601.03257
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12e129b1049decf9238a83496e442f0f992d1cbfa97ed007f9565d134e732925
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2026-01-07T00:00:00-05:00
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Primordial Black Hole Formation in $f(R)=R+\alpha R^2$ Gravity: Perturbative and Non-Perturbative Analysis
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arXiv:2601.02416v1 Announce Type: cross Abstract: We present a complete analytic and semi-analytic study of gravitational collapse and primordial black hole (PBH) formation in the quadratic $f(R)$ model $f(R)=R+\alpha R^2$. We first derive the perturbative expansion around General Relativity (GR), working to first order in the small parameter $\alpha$. For a collapsing flat FLRW dust interior we compute the explicit first-order corrections to the scale factor, the stellar radius, and the horizon formation time. We then use these results to obtain the shift in the PBH formation threshold $\delta_c$. The perturbative effect is small for PBHs forming in the deep radiation era, but becomes important when the background curvature is high. To access this early regime we reformulate the theory in the Einstein frame, where the model becomes GR plus the scalaron field $\phi$ with the Starobinsky potential. We provide the complete ODE system governing both the cosmological background and the evolution of an overdense closed FLRW patch. This system can be numerically integrated to obtain the critical overdensity $\delta_c(k)$ for PBH formation near the end of inflation.
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https://arxiv.org/abs/2601.02416
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d42194afc410a9e4ed34e37bbcd4670b77d33e585abfbd5c62cc63fd06ac3fd3
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2026-01-07T00:00:00-05:00
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Utilizing anticoincidence veto in a search for gravitational-wave transients
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arXiv:2601.02713v1 Announce Type: cross Abstract: We devise a technique to suppress the effect of noise transients occurring at gravitational-wave detectors based on temporal anticoincidence. Searches for gravitational-wave signals in the detector data are prone to spurious disturbances of terrestrial origin. The technique presented here benefits from the fact that such effects are generally non-coincident in time at geographically separated detectors. Therefore, abnormally loud triggers that are not time-coincident can be vetoed. We implement the veto technique in a matched-filter search for transient signals from binary black holes and observe search backgrounds to be generally close to the Gaussian limit. An improvement in the sensitivity of the search is demonstrated using simulated signals. The technique is expected to especially improve the detection efficiency of the search toward short duration transient signals.
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https://arxiv.org/abs/2601.02713
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fbb39f98bf29500308e8830b4fe281e485b20b8b32d6b47e298b08dd3d37b323
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2026-01-07T00:00:00-05:00
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A Universal Upper Bound on the Pressure-to-Energy Density Ratio in Neutron Stars
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arXiv:2601.02980v1 Announce Type: cross Abstract: The equation-of-state (EOS) parameter $\phi \equiv P/\varepsilon$, defined as the ratio of pressure to energy density, encapsulates the fundamental response of matter under extreme compression. Its value at the center of the most massive neutron star (NS), $\x \equiv \phi_{\rm c} = P_{\rm c}/\varepsilon_{\rm c}$, sets a universal upper bound on the maximum denseness attainable by any form of visible matter anywhere in the Universe. Remarkably, owing to the intrinsically nonlinear structure of the EOS in General Relativity (GR), this bound is forced to lie far below the naive Special Relativity (SR) limit of unity. In this work, we refine the theoretical upper bound on $\x$ in a self-consistent manner by incorporating, in addition to the causality constraint from SR, the mass-sphere stability condition associated with the mass evolution pattern in the vicinity of the NS center. This condition is formulated within the intrinsic-and-perturbative analysis of the dimensionless Tolman--Oppenheimer--Volkoff equations (IPAD-TOV) framework. The combined constraints yield an improved bound, $\x \lesssim 0.385$, which is slightly above but fully consistent with the previously derived causal-only limit, $\x \lesssim 0.374$. We further derive an improved scaling relation for NS compactness and verify its universality across a broad set of 284 realistic EOSs, including models with first-order phase transitions, exotic degrees of freedom, continuous crossover behavior, and deconfined quark cores. The resulting bound on $\x$ thus provides a new, EOS-independent window into the microphysics of cold superdense matter compressed by strong-field gravity in GR.
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https://arxiv.org/abs/2601.02980
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012f7b9f5d969479d6aa5e7cfd43aec239d9a0704dacf334813965de69478b1e
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2026-01-07T00:00:00-05:00
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Inflation in Extra-Dimensions with one or two branes
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arXiv:2601.02982v1 Announce Type: cross Abstract: In this paper, we study two inflationary models, namely, monomial inflation and the simplest $\alpha$-attractor inflation, within extra-dimensional frameworks. We consider three extra-dimensional setups: Dark Dimension, which embeds one flat extra-dimension to explain the observed smallness of the 4D cosmological constant $\Lambda_4$; and the two Randall-Sundrum scenarios with one warped extra-dimension, namely RS1 with two branes and RS2 with one brane. We derive the corresponding Friedmann equations, compute the slow-roll parameters in each case, and we fit the experimental data for ($n_s - 1$, $\alpha$, $\Delta_s^2$, $r$), using Planck, BICEP, and ACT data. We find that monomial inflation is strongly disfavored in all scenarios, while $\alpha$-attractor inflation provides an excellent fit to current observations, with extra-dimensional setups offering additional flexibility compared to the standard 4D case.
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https://arxiv.org/abs/2601.02982
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2026-01-07T00:00:00-05:00
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Standard Model Higgs Peaks: a Note on the Vacuum Instability during Inflation
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arXiv:2601.03231v1 Announce Type: cross Abstract: In the Standard Model, the Higgs potential develops an instability at high field values when the quartic self-coupling runs negative. Large quantum fluctuations during cosmic inflation could drive the Higgs field beyond the potential barrier, creating regions that would be catastrophic for our observable universe. We point out that the extreme-value statistics describing the peaks (maxima) of the Higgs values is the correct statistics to infer the condition to avoid vacuum instability. Even if this statistics delivers a bound on the Hubble rate during inflation which is only a factor $\sqrt{2}$ stronger than the one commonly adopted in the literature, it is qualitatively distinct and we believe worthwhile communicating it.
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https://arxiv.org/abs/2601.03231
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afaec7861ecb1daa1bb4281f958de0e583a25687260f29ff807dbbcd575fcc9b
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2026-01-07T00:00:00-05:00
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Extended Very-High-Energy Gamma-Ray Emission Surrounding PSR J0622 + 3749 Observed by LHAASO-KM2A
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arXiv:2106.09396v2 Announce Type: replace Abstract: We report the discovery of an extended very-high-energy (VHE) gamma-ray source around the location of the middle-aged (207.8 kyr) pulsar PSR J0622+3749 with the Large High Altitude Air Shower Observatory (LHAASO). The source is detected with a significance of $8.2\sigma$ for $E>25$~TeV assuming a Gaussian template. The best-fit location is (R.A., Dec.)$=(95^{\circ}\!.47\pm0^{\circ}\!.11,\,37^{\circ}\!.92 \pm0^{\circ}\!.09)$, and the extension is $0^{\circ}\!.40\pm0^{\circ}\!.07$. The energy spectrum can be described by a power-law spectrum with an index of ${-2.92 \pm 0.17_{\rm stat} \pm 0.02_{\rm sys} }$. No clear extended multi-wavelength counterpart of the LHAASO source has been found from the radio to sub-TeV bands. The LHAASO observations are consistent with the scenario that VHE electrons escaped from the pulsar, diffused in the interstellar medium, and scattered the interstellar radiation field. If interpreted as the pulsar halo scenario, the diffusion coefficient, inferred for electrons with median energies of $\sim160$~TeV, is consistent with those obtained from the extended halos around Geminga and Monogem and much smaller than that derived from cosmic ray secondaries. The LHAASO discovery of this source thus likely enriches the class of so-called pulsar halos and confirms that high-energy particles generally diffuse very slowly in the disturbed medium around pulsars.
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https://arxiv.org/abs/2106.09396
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91a71306a45eb5bfa503088f1130062bfca1f78e143bc1a9523e202bf121e8f5
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2026-01-07T00:00:00-05:00
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Discovery of the Ultra-high energy gamma-ray source LHAASO J2108+5157
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arXiv:2106.09865v3 Announce Type: replace Abstract: We report the discovery of a UHE gamma-ray source, LHAASO J2108+5157, by analyzing the LHAASO-KM2A data of 308.33 live days. Significant excess of gamma-ray induced showers is observed in both energy bands of 25-100 TeV and $\gt$100 TeV with 9.5 sigma and 8.5 sigma, respectively. This source is not significantly favored as an extensive source with the angular extension smaller than the point-spread function of KM2A. The measured energy spectrum from 20 to 200 TeV can be approximately described by a power-law function with an index of -2.83$\pm$ 0.18stat. A harder spectrum is demanded at lower energies considering the flux upper limit set by Fermi-LAT observations. The position of the gamma-ray emission is correlated with a giant molecular cloud, which favors a hadronic origin. No obvious counterparts have been found, deeper multiwavelength observations will help to shed new light on this intriguing UHE source.
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https://arxiv.org/abs/2106.09865
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952f90c278de7be3413c39b5aeccf2288d99e8aa4ab1a39c52ba14011b79a0fd
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2026-01-07T00:00:00-05:00
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Discovery of a new $\gamma$-ray source LHAASO J0341+5258 with emission up to 200TeV
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arXiv:2107.02020v4 Announce Type: replace Abstract: We report the discovery of a new unidentified extended $\gamma$-ray source in the Galactic plane named LHAASO J0341+5258 with a pre-trial significance of 8.2 standard deviations above 25 TeV. The best fit position is R.A.$=55.34^{\circ}\pm0.11^{\circ}$ and Dec$=52.97^{\circ}\pm0.07^{\circ}$. The angular size of LHAASO J0341+5258 is $0.29^\circ \pm 0.06^\circ_{stat} \pm0.02^\circ_{sys}$. The flux above 25 TeV is about $20\%$ of the flux of Crab Nebula. Although a power-law fit of the spectrum from 10 TeV to 200 TeV with the photon index $\alpha=2.98 \pm 0.19_{stat} \pm 0.02_{sys}$ is not excluded, the LHAASO data together with the flux upper limit at 10 GeV set by the Fermi LAT observation, indicate a noticeable steepening of an initially hard power-law spectrum %($\alpha \leq 1.75$) spectrum with a cutoff at $\approx 50$ TeV. We briefly discuss the origin of UHE gamma-rays. The lack of an energetic pulsar and a young SNR inside or in the vicinity of LHAASO J0341+5258 challenge, but do not exclude both the leptonic and hadronic scenarios of gamma-ray production.
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https://arxiv.org/abs/2107.02020
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e09a983249975f8cb49ca02c827b0cddcbe96b2800c927dafc6d3a2fd67f12c5
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2026-01-07T00:00:00-05:00
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Constraints on heavy decaying dark matter from 570 days of LHAASO observations
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arXiv:2210.15989v3 Announce Type: replace Abstract: The Kilometer Square Array~(KM2A) of the Large High Altitude Air Shower Observatory (LHAASO) aims at surveying the northern gamma-ray sky at energies above 10 TeV with unprecedented sensitivity. Gamma-ray observations have long been one of the most powerful tools for dark matter searches, as e.g., high-energy gamma-rays could be produced by the decays of heavy dark matter particles. In this letter, we present the first dark matter analysis with LHAASO-KM2A, using the first 340~days of data from 1/2-KM2A and 230~days of data from 3/4-KM2A. Several regions of interest are used to search for a signal and account for the residual cosmic-ray background after gamma/hadron separation. We find no excess of dark matter signals, and thus place some of the strongest gamma-ray constraints on the lifetime of heavy dark matter particles with mass between 10^5 and 10^9~GeV. Our results with LHAASO are robust, and have important implications for dark matter interpretations of the diffuse astrophysical high-energy neutrino emission.
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https://arxiv.org/abs/2210.15989
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1141e992bad239fc2691219addb71171f5da1bbf5e5bf1189bf634bc7d78490e
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2026-01-07T00:00:00-05:00
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An Ultrahigh-energy $\gamma$-ray Bubble Powered by a Super PeVatron
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arXiv:2310.10100v4 Announce Type: replace Abstract: We report the detection of a $\gamma$-ray bubble spanning at least 100$\rm deg^2$ in ultra high energy (UHE) up to a few PeV in the direction of the star-forming region Cygnus X, implying the presence Super PeVatron(s) accelerating protons to at least 10 PeV. A log-parabola form with the photon index $\Gamma (E) = (2.71 \pm 0.02) + (0.11 \pm 0.02) \times \log_{10} (E/10 \ {\rm TeV})$ is found fitting the gamma-ray energy spectrum of the bubble well. UHE sources, `hot spots' correlated with very massive molecular clouds, and a quasi-spherical amorphous $\gamma$-ray emitter with a sharp central brightening are observed in the bubble. In the core of $\sim 0.5^{\circ}$, spatially associating with a region containing massive OB association (Cygnus OB2) and a microquasar (Cygnus X-3), as well as previously reported multi-TeV sources, an enhanced concentration of UHE $\gamma$-rays are observed with 2 photons at energies above 1 PeV. The general feature of the bubble, the morphology and the energy spectrum, are reasonably reproduced by the assumption of a particle accelerator in the core, continuously injecting protons into the ambient medium.
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https://arxiv.org/abs/2310.10100
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e2448633ffbbe5fee01fa69a4bc56c02bc782e4a51c4dced91edd2b1ad4e1480
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2026-01-07T00:00:00-05:00
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Evidence for particle acceleration approaching PeV energies in the W51 complex
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arXiv:2407.00624v3 Announce Type: replace Abstract: The $\gamma$-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays (CRs) accelerated by the shock of supernova remnant (SNR) W51C and the dense molecular clouds in the adjacent star-forming region, W51B. However, the maximum acceleration capability of W51C for CRs remains elusive. Based on observations conducted with the Large High Altitude Air Shower Observatory (LHAASO), we report a significant detection of $\gamma$ rays emanating from the W51 complex, with energies from 2 TeV to 200 TeV. The LHAASO measurements, for the first time, extend the $\gamma$-ray emission from the W51 complex beyond 100 TeV and reveal a significant spectrum bending at tens of TeV. By combining the ``$\pi^0$-decay bump" featured data from Fermi-LAT, the broadband $\gamma$-ray spectrum of the W51 region can be well-characterized by a simple pp-collision model. The observed spectral bending feature suggests an exponential cutoff at $\sim400$~TeV or a power-law break at $\sim200$~TeV in the CR proton spectrum, most likely providing the first evidence of SNRs serving as CR accelerators approaching the PeV regime. Additionally, two young star clusters within W51B could also be theoretically viable to produce the most energetic $\gamma$ rays observed by LHAASO. Our findings strongly support the presence of extreme CR accelerators within the W51 complex and provide new insights into the origin of Galactic CRs.
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https://arxiv.org/abs/2407.00624
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8abb3ae8e0557dff0654d2acd71c71b266727c2361369b0b92bb0a5632f7db21
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2026-01-07T00:00:00-05:00
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An Enigmatic PeVatron in an Area around HII Region G35.6$-$0.5
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arXiv:2412.00379v2 Announce Type: replace Abstract: Identifying Galactic PeVatrons (PeV particle accelerators) from the ultra-high-energy (UHE, >100 TeV) $\gamma$-ray sources plays a crucial role in revealing the origin of Galactic cosmic rays. The UHE source 1LHAASO J1857+0203u is suggested to be associated with HESS J1858+020, which may be attributed to the possible PeVatron candidate supernova remnant (SNR) G35.6$-$0.4 or HII region G35.6$-$0.5. We perform detailed analysis on the very-high-energy and UHE $\gamma$-ray emissions towards this region with data from the Large High Altitude Air Shower Observatory (LHAASO). 1LHAASO J1857+0203u is detected with a significance of 11.6$\sigma$ above 100 TeV, indicating the presence of a PeVatron. It has an extension of $\sim 0.18^\circ$ with a power-law (PL) spectral index of $\sim$2.5 in 1-25 TeV and a point-like emission with a PL spectral index of $\sim$3.2 above 25 TeV. Using the archival CO and HI data, we identify some molecular and atomic clouds that may be associated with the TeV $\gamma$-ray emissions. Our modelling indicates that the TeV $\gamma$-ray emissions are unlikely to arise from the clouds illuminated by the protons that escaped from SNR G35.6$-$0.4. In the scenario that HII region G35.6$-$0.5 could accelerate particles to the UHE band, the observed GeV-TeV $\gamma$-ray emission could be well explained by a hadronic model with a PL spectral index of $\sim$2.0 and cutoff energy of $\sim$450 TeV. However, an evolved pulsar wind nebula origin cannot be ruled out.
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https://arxiv.org/abs/2412.00379
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1ac0abd0ead7139f7f86adde05723f283d9b21bb1428eeeee2f65fa3557eaaa8
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2026-01-07T00:00:00-05:00
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Cross-correlating the patchy screening and kinetic Sunyaev-Zel'dovich effects as a new probe of reionization
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arXiv:2501.07623v3 Announce Type: replace Abstract: The kinetic Sunyaev-Zel'dovich effect (kSZ) and patchy screening effect are two complementary cosmic microwave background (CMB) probes of the reionization era. The kSZ effect is a relatively strong signal, but is difficult to disentangle from other sources of temperature anisotropy, whereas patchy screening is weaker but can be reconstructed using the cleaner polarization channel. Here, we explore the potential of using upcoming CMB surveys to correlate a reconstructed map of patchy screening with (the square of) the kSZ map, and what a detection of this cross-correlation would mean for reionization science. To do this, we use simulations and theory to quantify the contributions to this signal from different redshifts. We then use the expected survey properties for CMB-S4 and CMB-HD to make detection forecasts. We find that, for or our fiducial reionization scenario, CMB-S4 will obtain a hint of this signal at up to 1.8$\sigma$, and CMB-HD will detect it at up to 14$\sigma$. We explore the physical interpretation of the signal and find that it is uniquely sensitive to the first half of reionization and to the bispectrum of the ionized gas distribution.
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https://arxiv.org/abs/2501.07623
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90ec017f793d58a4047fe1c049db64c723f85b51ffd4ed2004f0a2dafda1f127
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2026-01-07T00:00:00-05:00
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Constraining the Cosmic-ray Energy Based on Observations of Nearby Galaxy Clusters by LHAASO
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arXiv:2502.16499v2 Announce Type: replace Abstract: Galaxy clusters act as reservoirs of high-energy cosmic rays (CRs). As CRs propagate through the intracluster medium, they generate diffuse $\gamma$-rays detectable by arrays such as LHAASO. These $\gamma$-rays result from proton-proton ($pp$) collisions of very high-energy cosmic rays (VHECRs) or inverse Compton (IC) scattering of positron-electron pairs created by $p\gamma$ interactions of ultra-high-energy cosmic rays (UHECRs). We analyzed diffuse $\gamma$-ray emission from the Coma, Perseus, and Virgo clusters using LHAASO data. Diffuse emission was modeled as a disk of radius $R_{500}$ for each cluster while accounting for point sources. No significant diffuse emission was detected, yielding 95\% confidence level (C.L.) upper limits on the $\gamma$-ray flux: for WCDA (1-25~TeV) and KM2A ($>25$~TeV), less than $(49.4, 13.7, 54.0)$ and $(1.34, 1.14, 0.40) \times 10^{-14}$~ph~cm$^{-2}$~s$^{-1}$ for Coma, Perseus, and Virgo, respectively. The $\gamma$-ray upper limits can be used to derive model-independent constraints on the integral energy of CRp above 10~TeV (corresponding to the LHAASO observational range $>1$~TeV under the $pp$ scenario) to be less than $(1.96, 0.59, 0.08) \times 10^{61}$~erg. The absence of detectable annuli/ring-like structures, indicative of cluster accretion or merging shocks, imposes further constraints on models in which the UHECRs are accelerated in the merging shocks of galaxy clusters.
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https://arxiv.org/abs/2502.16499
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868aa80fc99a9fd1d9c2f75d74ac71e24c26f85e677cd6942c8f1e1e9a97db55
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2026-01-07T00:00:00-05:00
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Unifying Circumstellar Environment in Broad-Lined Type Ic Radio Supernovae Towards Off-axis Gamma-Ray Burst Exploration
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arXiv:2503.13291v2 Announce Type: replace Abstract: Decades have passed since the first confirmed association between a broad-lined Type Ic supernova (Type IcBL SN) and a long gamma-ray burst (GRB), and the number of known GRB-SN associations has steadily increased. However, it is important to note that the radiation from GRB afterglows and the radio emission from SNe may be both produced by outflows evolving within the same ambient medium. In this study, we present the first comprehensive theoretical predictions of radio emission from a Type IcBL supernova associated with a GRB jet, explicitly accounting for the structure of the ambient medium. We model each component of the radio emission, with particular emphasis on exploring wide ranges of isotropic explosion energy and viewing angle in our GRB afterglow calculations. We show that, within specific regions of parameter space, the composite radio light curve exhibits a characteristic double-peaked structure. This clear double-peaked feature emerges when either (1) the isotropic explosion energy is small (low-luminosity GRB) or (2) the viewing angle is large (off-axis GRB). Our results demonstrate that follow-up radio observations carried out within a few years of the optical discovery of nearby Type IcBL SNe (-100 Mpc) can provide a unique diagnostic of off-axis GRBs that would otherwise remain undetected in Type IcBL SNe. This represents a step toward revealing the nature of long GRB progenitors and clarifying their connection to Type IcBL SNe.
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https://arxiv.org/abs/2503.13291
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806fbb1979c72db8a03dfaca95ace97b98304097e9ddd4bd0184eedb2d361dd4
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2026-01-07T00:00:00-05:00
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Water ice in the debris disk around HD 181327
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arXiv:2505.08863v2 Announce Type: replace Abstract: Debris disks are exoplanetary systems that contain planets, minor bodies (i.e., asteroids, Kuiper belt objects, comets, etc.), and micron-sized debris dust. Since water ice is the most common frozen volatile, it plays an essential role in the formation of planets and minor bodies. Although water ice has been commonly found in Kuiper belt objects and comets in the Solar System, no definitive evidence for water ice in debris disks has been obtained to date. Here, we report the discovery of water ice in the HD 181327 disk using the James Webb Space Telescope Near-Infrared Spectrograph. We detect the solid-state broad absorption feature of water ice at 3 $\mu$m and a distinct Fresnel peak feature at 3.1 $\mu$m, a characteristic of large water-ice particles. This implies the presence of a water-ice reservoir in the HD 181327 exoKuiper belt. Gradients of water-ice features at different stellocentric distances reveal a dynamic process of destroying and replenishing water ice in the disk, with estimated water-ice mass fractions ranging from 0.1% at ~85 au to 14% at ~113 au. It is highly plausible that the icy bodies that release water ice in HD 181327 could be the extra-solar counterparts of some of the Kuiper belt objects in our Solar System, supported by their spectral similarity.
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https://arxiv.org/abs/2505.08863
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9fadd9f1995df134475b76b37624dc83d50263d48395757fa568c6f520a57e75
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2026-01-07T00:00:00-05:00
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Going beyond $S_8$: fast inference of the matter power spectrum from weak-lensing surveys
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arXiv:2506.16434v3 Announce Type: replace Abstract: Weak lensing surveys are often summarized by constraints on the derived parameter ${S_8\equiv\sigma_8\sqrt{\Omega_{\rm m}/0.3}}$, obscuring the rich scale and redshift information encoded in the data, and limiting our ability to identify the origin of any tensions with $\Lambda$CDM predictions from the cosmic microwave background. In this work, we introduce a fast and flexible framework to extract the scale-dependent matter power spectrum $P(k, z)$ from cosmic shear and CMB lensing measurements, parameterizing deviations from the Planck $\Lambda$CDM prediction as a free function $\alpha(k)$. Using public data from DES Y3, KiDS-1000, HSC Y3, and ACT DR6, we constrain $\alpha(k)$ with fast Hamiltonian Monte Carlo inference, employing multipoles up to $\ell_{\rm max}\sim2000$ for the galaxy lensing surveys. Our results show a consistent 15-30% suppression in the matter power spectrum at intermediate scales ($k \sim 0.1-1{\rm Mpc}^{-1}$) in galaxy-lensing data relative to a Planck $\Lambda$CDM prediction with a CDM-only (no baryonic feedback) power spectrum, with combined tensions reaching up to $4\sigma$. This is under a fixed cosmology and with analytic marginalization over shear and redshift calibration uncertainties. In contrast, ACT CMB lensing is consistent with $\Lambda$CDM at ${k\lesssim 0.1 {\rm Mpc}^{-1}}$. We validate our method using mock data, quantify consistency between datasets, and demonstrate how the resulting $\alpha(k)$ likelihoods can be used to test specific models for the power spectrum. All code, data products, and derived likelihoods are publicly released. Our results highlight the importance of reporting lensing constraints on $P(k, z)$ and pave the way for model-agnostic test of growth of structure with upcoming surveys such as LSST, Euclid, and Roman.
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https://arxiv.org/abs/2506.16434
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1370a7104db1cf6191c1b627d2a01536330193f65af8581fcd37a0bd2361703d
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2026-01-07T00:00:00-05:00
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Constraining the Stellar-to-Halo Mass Relation with Galaxy Clustering and Weak Lensing from DES Year 3 Data
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arXiv:2506.22367v3 Announce Type: replace Abstract: We develop a framework to study the relation between the stellar mass of a galaxy and the total mass of its host dark matter halo using galaxy clustering and galaxy-galaxy lensing measurements. We model a wide range of scales, roughly from $\sim 100 \; {\rm kpc}$ to $\sim 100 \; {\rm Mpc}$, using a theoretical framework based on the Halo Occupation Distribution and data from Year 3 of the Dark Energy Survey (DES) dataset. The new advances of this work include: 1) the generation and validation of a new stellar mass-selected galaxy sample in the range of $\log M_\star/M_\odot \sim 9.6$ to $\sim 11.5$; 2) the joint-modeling framework of galaxy clustering and galaxy-galaxy lensing that is able to describe our stellar mass-selected sample deep into the 1-halo regime; and 3) stellar-to-halo mass relation (SHMR) constraints from this dataset. In general, our SHMR constraints agree well with existing literature with various weak lensing measurements. We constrain the free parameters in the SHMR functional form $\log M_\star (M_h) = \log(\epsilon M_1) + f\left[ \log\left( M_h / M_1 \right) \right] - f(0)$, with $f(x) \equiv -\log(10^{\alpha x}+1) + \delta [\log(1+\exp(x))]^\gamma / [1+\exp(10^{-x})]$, to be $\log M_1 = 11.506^{+0.325}_{-0.404}$, $\log \epsilon = -1.632^{+0.306}_{-0.181}$, $\alpha = -1.638^{+0.108}_{-0.099}$, $\gamma = 0.596^{+0.251}_{-0.210}$ and $\delta = 3.810^{+2.045}_{-1.811}$. The inferred average satellite fraction is within $\sim 5-35\%$ for our fiducial results and we do not see any clear trends with redshift or stellar mass. Furthermore, we find that the inferred average galaxy bias values follow the generally expected trends with stellar mass and redshift. Our study is the first SHMR in DES in this mass range, and we expect the stellar mass sample to be of general interest for other science cases.
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https://arxiv.org/abs/2506.22367
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a637454e0f1f8eb26516b6cbb6892b6186403740678e8d292afbc47bfac683a8
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2026-01-07T00:00:00-05:00
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Helium Atmospheres May Hide in Current Exoplanet Analysis Frameworks
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arXiv:2506.22537v2 Announce Type: replace Abstract: The increasing number of detailed exoplanet observations offers an opportunity to refine our analyses and interpretations. Here, we show that atmospheres that appear volatile-rich and/or cloudy may instead be helium-rich. As transmission spectra constrain the atmospheric scale height ($H$), a He-enriched atmosphere can be misinterpreted as H$_2$-dominated water-rich to bring the mean molecular weight ($\mu$) to intermediate values ($\sim$4$-$10) when He/H$_2$ is fixed. Similarly, a cloud deck can reduce the spectral features, and thus the apparent (i.e., cloud-free equivalent) $H$. We present a proof-of-concept reanalysis of HD~209458~b's JWST transmission spectrum treating He/H$_2$ as a free parameter, resulting in sets of He-rich solutions. We argue that He enhancement must be considered to reliably constrain atmospheric composition, be sensitive to a more diverse planetary population, and ultimately yield robust trends to inform formation and evolution pathways. Looking ahead, we suggest leveraging insights from differences in pressure-broadening effects, outflow measurements, and atmospheric chemistry to disentangle reliably between He-, volatile-rich, and cloudy atmospheres -- while recognizing that associated models need targeted upgrades to reach the fidelity level required to this end.
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https://arxiv.org/abs/2506.22537
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a9f5500a4694af239f9cf2b0f8c3c040ddc9943de1bddc9e4d530004c75805fa
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2026-01-07T00:00:00-05:00
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Effective Theories of Redshift-Space Galaxy Peculiar Velocities
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arXiv:2508.00066v2 Announce Type: replace Abstract: We present predictions for redshift-space peculiar velocity statistics in the Lagrangian and Eulerian formulations of the effective field theory (EFT) of large-scale structure. We compute 2-point pairwise velocity statistics up to the second moment at next-to-leading (1-loop) order, showing that they can be modeled together with redshift-space galaxy densities with a consistent set of EFT coefficients. We show that peculiar velocity statistics have a distinct dependence on long-wavelength bulk flows that necessitates a variation on the usual infrared (IR) resummation procedure used to model baryon acoustic oscillations (BAO) in galaxy clustering. This can be implemented recursively in powers of the velocity in both the Lagrangian and Eulerian frameworks. We validate our analytic calculations against fully nonlinear N-body simulations, demonstrating that they can be used to recover the growth rate at better than percent level precision, well beyond the statistical requirements of upcoming peculiar velocity surveys and measurements of the kinetic Sunyaev-Zeldovich (kSZ) effect. As part of this work, we release $\href{https://github.com/sfschen/velocisaurus}{\texttt{velocisaurus}}$, a fast $\texttt{Python}$ code for computing EFT predictions of peculiar velocity statistics.
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https://arxiv.org/abs/2508.00066
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2094721398e9fbee69b5d36799267cdf0268b38ac101daa87bc8035eda1264d9
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2026-01-07T00:00:00-05:00
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Cosmological Constraints on $f(T,B)$ Gravity from Observations of Early and Late Universe
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arXiv:2508.01652v2 Announce Type: replace Abstract: This study proposes a unified framework comprising two complementary approaches to constrain three functional forms of $f(T,B)$ gravity, namely the linear, quadratic, and general power law models, by jointly utilizing early and late Universe observations. First, we impose bounds on deviations in the weak interaction freeze-out temperature, informed by the latest measurements of the primordial helium-4 mass fraction. Second, we incorporate direct Hubble parameter data, $H(\mathcal{z})$, obtained from Cosmic Chronometers in the redshift range $0.07\le\mathcal{z}\le2.0$, to trace the expansion history of the Universe. By minimizing a combined chi-square statistic across both datasets, we derive the best-fit values and confidence intervals for each model parameter. The joint analysis significantly refines the parameter constraints compared to methods based solely on Big Bang Nucleosynthesis, thereby offering a more robust test of $f(T,B)$ gravity across cosmic epochs. The results support the viability of torsion-based modifications to General Relativity and provide a consistent methodology for future evaluation using upcoming observational data.
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https://arxiv.org/abs/2508.01652
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69e2c68d6145af271d05ad130cd62975f2c45141f2f89f7d9d236d5478e927e6
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2026-01-07T00:00:00-05:00
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Supermassive black hole growth from stellar binary encounters
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arXiv:2509.02316v3 Announce Type: replace Abstract: The growth of supermassive black holes (SMBHs) remains a central problem in astrophysics, with current observations providing only limited constraints on the underlying mechanisms. One possible growth channel is stellar accretion via the Hills mechanism, wherein a SMBH tidally breaks up a passing binary star, capturing and eventually accreting a member of the binary. We adopt a framework based on kinematics to predict capture rates from parameters that include the central number density of stars, the stellar velocity dispersion, the binary fraction, and black hole mass. We then estimate the growth of SMBHs across a range of galactic environments. In a data set of 91 galaxies of various types and masses, we identify two candidates with SMBHs for which stellar accretion may be a driver of growth. Closer to home, a recent analysis of observed hypervelocity stars from the Large Magellanic Cloud (LMC) implicates binary star interactions with a massive black hole. Every hypervelocity star produced in this way leaves a bound partner that may be accreted, providing an active growth channel for the LMC's black hole.
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https://arxiv.org/abs/2509.02316
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fb3aeee654881d60b517c86599c6188162415a1e28e1b45981b2675ecc2869e6
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2026-01-07T00:00:00-05:00
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A census of quiescent galaxies across $0.5 < z < 8$ with JWST/MIRI: Mass-dependent number density evolution of quiescent galaxies in the early Universe
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arXiv:2510.12235v2 Announce Type: replace Abstract: Recent JWST observations have revealed a large population of quiescent galaxies (QGs) at high redshift ($z \sim 4-8$), challenging current models of early galaxy formation and quenching. Accurate number density estimates are crucial but remain uncertain. We present a systematic study of QGs at $0.5 5$ that are often missed without including MIRI data. We find that the evolution of the QG number density is strongly mass-dependent. The density of massive QGs ($\log (M_{\star}/M_{\odot}) > 10.6$) declines rapidly, falling from $n \approx 1.32\times10^{-5}~~\mathrm{Mpc^{-3}}$ at $z \sim 3-4$ to $n 6$. In contrast, low-mass QGs ($9.5 4$ and fail to reproduce the flat density evolution observed for the low-mass population.
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https://arxiv.org/abs/2510.12235
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49264ea2c22a4b546748d995717237fb3129439046bce5eeb40edc05f5137b2e
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2026-01-07T00:00:00-05:00
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Forecasts of constraining isotropic cosmic birefringence on AliCPT-1
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arXiv:2510.21221v2 Announce Type: replace Abstract: Cosmic birefringence (CB) is a promising probe of parity-violating physics beyond the Standard Model, characterized by the rotation of the linear polarization plane of cosmic microwave background (CMB) photons. This effect, quantified by the birefringence angle $\beta$, generates non-zero $EB$ and $TB$ correlations that are otherwise absent in standard cosmology. However, instrumental miscalibration angles $\alpha$ can mimic this signal, necessitating a joint estimation approach. In this work, we forecast the sensitivity of the AliCPT experiment, combined with Planck HFI data, on constraining the isotropic CB angle using a semi-analytical maximum-likelihood method. We simulate observations under various foreground complexities, rotation angles, and scanning strategies, and demonstrate that AliCPT can achieve an uncertainty of $\sigma(\beta)=0.09^\circ$ with one-year data, which will improve to $0.026^\circ$ after four years' observations. We also find that neglecting or mismodeling the foreground $EB$ correlation will introduce significant biases, which can be alleviated under a clean but small sky patch.
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https://arxiv.org/abs/2510.21221
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d3aae3c757311e81c1eea84eed1d52e1b5677ec57315e28829d8a79e7e943333
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2026-01-07T00:00:00-05:00
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The Advanced X-ray Imaging Satellite (AXIS) Community Science Book
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arXiv:2511.00253v2 Announce Type: replace Abstract: The AXIS Community Science Book represents the collective effort of 592 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles 138 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks.
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https://arxiv.org/abs/2511.00253
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Academic Papers
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c25f7e8efee87a47956c2dd1c7a6c031a220820a9cb22592372d8bb1ac207f20
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2026-01-07T00:00:00-05:00
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LHAASO Detection of Ultra-High-Energy Gamma-Ray Emission toward the Giant Molecular Clouds
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arXiv:2511.05015v2 Announce Type: replace Abstract: The $\gamma$-ray from Giant molecular clouds (GMCs) is regarded as the most ideal tool to perform in-situ measurement of cosmic ray (CR) density and spectra in our Galaxy. We report the first detection of $\gamma$-ray emissions in the very-high-energy (VHE) domain from the five nearby GMCs with a stacking analysis based on a 4.5-year $\gamma$-ray observation with the Large High Altitude Air Shower Observatory (LHAASO) experiment. The spectral energy distributions derived from the GMCs are consistent with the expected $\gamma$-ray flux produced via CR interacting with the ISM in the energy interval 1 - 100 $~\rm$ TeV. In addition, we investigate the presence of the CR spectral `knee' by introducing a spectral break in the $\gamma$-ray data. While no significant evidence for the CR knee is found, the current KM2A measurements from GMCs strongly favor a proton CR knee located above 0.9$~\rm$ PeV, which is consistent with the latest measurement of the CR spectrum by ground-based experiments.
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https://arxiv.org/abs/2511.05015
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Academic Papers
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29cc48bc1c9fcbf5d7d7fe8a0412fff39f1a9653e1c7d759bda2b7ad5ef7a887
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2026-01-07T00:00:00-05:00
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Supermassive Dark Stars and their remnants as a possible solution to three recent cosmic dawn puzzles
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arXiv:2511.08477v2 Announce Type: replace Abstract: The James Webb Space Telescope (JWST) has begun to revolutionize our view of the Cosmos. The discovery of Blue Monsters (i.e., ultra-compact yet very bright high-z galaxies) and the Little Red Dots (i.e., very compact dustless strong Balmer break cosmic dawn sources) pose significant challenges to pre-JWST era models of the assembly of first stars and galaxies. In addition, JWST data further strengthen the problem posed by the origin of the supermassive black holes that power the most distant quasars observed. Stars powered by Dark Matter annihilation (i.e., Dark Stars) can form out of primordial gas clouds during the cosmic dawn era and subsequently might grow via accretion and become supermassive. In this paper we argue that Supermassive Dark Stars (SMDSs) offer natural solutions to the three puzzles mentioned above.
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https://arxiv.org/abs/2511.08477
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Academic Papers
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170833a5c9d40e89091e4dec3dfe87bfae82cd6c6f044ddd7fbcb77abea5b9fc
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2026-01-07T00:00:00-05:00
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Delayed Wind Onset in Pa 30, the Remnant of Type Iax SN 1181
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arXiv:2511.14829v2 Announce Type: replace Abstract: Pa 30 is the recently identified remnant of the historical supernova SN 1181, likely a Type Iax event, and a nebula surrounding the central white dwarf launching a fast wind ($\sim10^9~\cm~\s^{-1}$) is observed in optical and infrared bands. X-ray observations show that this wind collides with the surrounding material and produces a termination shock, and the observed extent of the shock indicates that the wind started blowing centuries after 1181 A.D. rather than immediately after the SN explosion. We propose that the wind is triggered by delayed ignition of fallback carbon-rich material on the WD surface and investigate the conditions that reproduce such delayed ignition. We show that producing delays of several centuries requires a relatively hot post-explosion WD core with a temperature $T_c \simeq 6\times10^8~\mathrm{K}$. This supports the pure-deflagration progenitor scenario for Type Iax SN 1181, which implies the presence of a He star companion inside Pa~30; we also discuss why such a potential He star has not been detected and its prospects for discovery by future observations.
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https://arxiv.org/abs/2511.14829
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Academic Papers
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96c9e5c1d778ad6f447a3e3651823c6cd8b831235b6dbaccfcd1dd0590d677d3
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2026-01-07T00:00:00-05:00
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Galactic bars are already mature at Cosmic Noon: bar strength and flatness at z ~ 1.5
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arXiv:2512.04163v2 Announce Type: replace Abstract: In this work, we explore the nature of $z>1$ galactic bars. Once thought to be highly transient, our results demonstrate otherwise. Our sample consists of nine massive ($>10^{10.5}\,\rm M_{\odot}$) star-forming barred-spiral galaxies at $z_{\rm spec} \sim 1.5$. Using rest-frame near-IR (F444W) JWST/NIRCam imaging, we apply ellipse fitting along with 1D and 2D morphological modeling to directly measure bar properties. We find that five galaxies host flat surface brightness profiles (bar S\'ersic index $<0.4$), indicative of highly evolved, "mature" bars. By contrast, only two galaxies show exponential profiles, characteristic of young bars, and these are also shorter in absolute length than the flat bars. We therefore conclude that a large fraction of bars at this epoch have already matured, thereby indicating the presence of well-settled disks required to facilitate bar formation and sustained evolution well before $z\sim1.5$. To assess the gravitational impact of the bars, we calculate the maximum transverse-to-radial force ratio ($Q_{b}$). We find that $Q_{b}$ values are comparable to, or weaker than, those of bars in the local Universe, Seven of the nine bars show only a marginal increase in strength with maturity (from exponential to flat bars). Contrarily however, the remaining two bars are flat, but have the lowest $Q_{b}$ values in our sample. We hence propose that the mature bars at $z\sim 1.5$ may experience phases of weakening due to rapid gas inflows and/or minor mergers. In conclusion, our work sheds light on the rapidly evolving nature of high-z bars and paves the way for larger statistical studies.
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https://arxiv.org/abs/2512.04163
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Academic Papers
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e05e30d19b5c99ed0f5284b0e8fae358093f451a7b3639912a3ee868a94eaa97
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2026-01-07T00:00:00-05:00
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Squared-field cross-correlation between kinetic Sunyaev-Zel'dovich effect and 21-cm intensity mapping
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arXiv:2512.05588v2 Announce Type: replace Abstract: Neutral hydrogen (HI) 21-cm intensity mapping is an effective method to track the distribution of baryonic matter, and extract astrophysical and cosmological information. The 21-cm intensity field has a nonvanishing cross-correlation with the kinetic Sunyaev-Zel'dovich (kSZ) effect that traces the velocity and density perturbations of free electrons. By using the linear perturbation theory, in this paper we calculate analytically, for the first time, the cross-correlation between the squared kSZ field and the projection of the squared HI intensity mapping field with the flat-sky approximation. This statistic remains nonvanishing even after the long-wavelength line-of-sight modes ($k_{\parallel}$) are removed due to foreground contamination. We further forecast for the prospects of detection with the SKA-MID 21-cm intensity mapping experiments (redshifts in range of $0.3 < z < 1$), and the kSZ maps measured by the Atacama Cosmology Telescope (ACT) and Simons Observatory (SO). The predicted cumulative signal-to-noise ratio is $1.92$ for SKA-ACT and $3.99$ for SKA-SO. These results show a possible on-the-edge detection on the cross-correlation signal at low redshifts, which in turn could serve as a validation step toward using it for the Epoch of Reionization studies.
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https://arxiv.org/abs/2512.05588
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Academic Papers
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ffb840ee15c97c43595cc73db8dcac5ea1adb899d8e2cc45a3104c0fbc75cb23
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2026-01-07T00:00:00-05:00
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A high-dynamic-range view of the growth of structure and the warm/hot Universe
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arXiv:2512.13818v2 Announce Type: replace Abstract: Baryons heat to temperatures above $>\!\!10^5\,\mathrm{K}$ as they accrete onto massive overdensities -- galaxies, groups, clusters, and filaments -- where they ionize and become optically transparent. Deep mm-wave observations such as those with ALMA have begun to probe a handful ($\sim\,$4) of massive systems at $z\!\sim\!2-4$, while low-resolution mm-wave surveys have detected thousands of objects at arcminute resolution out to $z\!\approx\!2$. To truly advance the field of the evolution of large-scale structures, mapping the warm/hot distribution of ionized gas out to the redshift of their formation, the ESO community requires a large-aperture single-dish (sub-)mm telescope. This will need to provide several orders of magnitude higher mapping speeds than currently available while preserving the few arcsecond resolution required for imaging the gas and removing contaminating radio and dusty thermal signals across the full (sub-)mm wavelength range.
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https://arxiv.org/abs/2512.13818
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Academic Papers
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2a2182ee239af975af200fb61b4b357fe9eb447ab2fd16fe51a854bcee763d14
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2026-01-07T00:00:00-05:00
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Decoding Cygnus X-2: The Critical Role of Reflection in IXPE Data
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arXiv:2601.01669v2 Announce Type: replace Abstract: We present a spectro-polarimetric re-analysis of the first IXPE observation of Cygnus X-2 which we determine to be mainly in the normal branch, from quasi-simultaneous observations with NuSTAR, NICER, and INTEGRAL. We measure the hard X-ray polarization angle and find it to be consistent with the previously measured position angle of the radio jet. Leveraging NuSTAR's detection of both the relativistic Fe K emission line and the Compton hump, we constrain the flux contribution of the reflected emission from the inner accretion disk to be 10% of the total X-ray flux in the IXPE energy band. Unlike previous studies that modeled only the Fe K emission line, we fit the full-band reflection spectrum using a fully relativistic disk model. There is strong degeneracy between the Comptonized and reflection components. Given that the Comptonized component is not expected to be highly polarized, a polarization degree of approximately 20% for the reflection component could explain the X-ray polarization data from IXPE. We also discuss the disk inclination angle inferred from our spectro-polarimetric modeling, as well as other possible explanations for the data.
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https://arxiv.org/abs/2601.01669
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Academic Papers
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9a55938b430fffee0d1d4cd7eb179c19431cd7f13159cc19bc8ecf99990d1a7c
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2026-01-07T00:00:00-05:00
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Inferring physical parameters of solar filaments from simultaneous longitudinal and transverse oscillations
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arXiv:2601.01730v2 Announce Type: replace Abstract: Context. Different modes of oscillations are frequently observed in solar prominences/filaments, and prominence seismology helps estimate important physical parameters like the magnetic field strength. Although the simultaneous detection of longitudinal and transverse oscillations in the same filament is not common, such rare observations provide a unique opportunity to constrain the physical parameters of interest. Aims. In this study, we aim to estimate the physical parameters of prominences undergoing simultaneous longitudinal and transverse oscillations. Methods. We apply Bayesian seismology techniques to observations of longitudinal and transverse filament oscillations to infer the magnetic field strength, the length, and the number of twists in the flux tube holding the prominence plasma. We first use the observations of longitudinal oscillations and the pendulum model to infer the posterior probability density for the magnetic field strength. The obtained marginal posterior of the magnetic field, combined with the observations of the transverse oscillations, is then used to estimate the probable values of the length of the magnetic flux tube that supports the filament material using Bayesian inference. This estimated length is used to compute the number of twists in the flux tube. Results. For the prominences under study, we find that the length of the flux tubes supporting the quiescent prominences can be very large (from 100 to 1000 Mm) and the number of twists in the flux tube are not more than three. Conclusions. Our results demonstrate that Bayesian analysis offers valuable methods to perform parameter inference in the context of prominence seismology.
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https://arxiv.org/abs/2601.01730
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Academic Papers
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a117e95e15e5081280bad99989faa2470b81c6d725e17672ed6b68c3250c1315
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2026-01-07T00:00:00-05:00
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The Betelgeuse Enigma: The Betelbuddy Hypothesis
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arXiv:2601.02012v2 Announce Type: replace Abstract: In the past six years, Betelgeuse has been in the news and drawn significant public interest. Starting in October 2019, Betelgeuse underwent a striking dimming event, fading from magnitude 0.5 to 1.7 by mid February 2020 a threefold decrease in brightness This gave rise to a number of speculative debates that the star was on the verge of a supernova, a moment of eerie quiet before the cosmic outburst. In a previous article, the author discussed the most accepted explanation to the dimming caused by episodic mass loss that released large dust grains, which obscured Betelgeuse's light and made it appear fainter. This interpretation suggested that the dimming was not a precursor to a supernova, as Betelgeuse is likely still far from reaching that stage. On 21 July 2025, the existence of the companion star was confirmed with direct imaging, for the first time, by the alopeke instrument on the 8.1 m Gemini North telescope. The companion is 6 magnitudes fainter than Betelgeuse and orbits close to Betelgeuse itself, within the supergiant star's extended outer atmosphere. The stellar companion was detected at an angular separation of 52 mas and a position angle of 115 deg east of north. These measurements, along with its brightness, being roughly 6 magnitudes fainter than Betelgeuse at 466 nm, are in excellent agreement with dynamical predictions. Although this was only a 1.5 sigma detection, the agreement in the companion's appearance, separation, position angle, magnitude difference, and estimated mass is reasonable, making the result tentatively acceptable. The next optimum period for observations is November 2027, when we hope to get better observations. This article describes the interesting twists and turns of this study and what lies in the future for Betelgeuse and its companion, Betelbuddy or Siwarha.
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https://arxiv.org/abs/2601.02012
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Academic Papers
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6bbb9b2ad1bf308cb6d3c90d89def157b1aa1881d191fe21c55929d7f314c99a
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2026-01-07T00:00:00-05:00
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Measurement of attenuation length of the muon content in extensive air showers from 0.3 to 30 PeV with LHAASO
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arXiv:2410.13173v3 Announce Type: replace-cross Abstract: The attenuation length of the muon content in extensive air showers provides important information regarding the generation and development of air showers. This information can be used not only to improve the description of such showers but also to test fundamental models of hadronic interactions. Using data from the LHAASO-KM2A experiment, the development of the muon content in high-energy air showers was studied. The attenuation length of muon content in the air showers was measured from experimental data in the energy range from 0.3 to 30 PeV using the constant intensity cut method. By comparing the attenuation length of the muon content with predictions from high-energy hadronic interaction models (QGSJET-II-04, SIBYLL 2.3d, and EPOS-LHC), it is evident that LHAASO results are significantly shorter than those predicted by the first two models (QGSJET-II-04 and SIBYLL 2.3d) but relatively close to those predicted by the third model (EPOS-LHC). Thus, the LHAASO data favor the EPOS-LHC model over the other two models. The three interaction models confirmed an increasing trend in the attenuation length as the cosmic-ray energy increases.
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https://arxiv.org/abs/2410.13173
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Academic Papers
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ef498377368025826a384461a8e830da113ee5c6173a985aaa1df1c9362b1264
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2026-01-07T00:00:00-05:00
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Dipole Polarizability of Finite Nuclei as a Probe of Neutron Stars
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arXiv:2503.17143v3 Announce Type: replace-cross Abstract: Nuclear ground state and collective excitation properties provide a means to probe the nuclear matter equation of state and establish connections between observables in finite nuclei and neutron stars. Specifically, the electric dipole polarizability, measured with high precision in various neutron-rich nuclei, serves as a robust constraint on the density dependence of the symmetry energy. In this Letter, we employ a class of relativistic energy density functionals in a twofold process: first, to link the electric dipole polarizability from recent experiments to the slope of the symmetry energy, and second, to translate this information into constraints on the tidal deformability and radii of neutron stars, in connection with multimessenger astrophysical observations from pulsars and binary neutron stars. We provide compelling evidence that the electric dipole polarizability represents a key nuclear observable to probe the neutron star properties. By significantly reducing the uncertainties in the mass-radius plane, our findings also align with recent multimessenger observations.
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https://arxiv.org/abs/2503.17143
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Academic Papers
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