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galaxy groups and poor clusters are more common than rich clusters, and host the largest fraction of matter content in the universe. hence, their studies are key to understand the gravitational and thermal evolution of the bulk of the cosmic matter. moreover, because of their shallower gravitational potential, galaxy groups are systems where non-gravitational processes (e.g., cooling, agn feedback, star formation) are expected to have a higher impact on the distribution of baryons, and on the general physical properties, than in more massive objects, inducing systematic departures from the expected scaling relations. despite their paramount importance from the astrophysical and cosmological point of view, the challenges in their detection have limited the studies of galaxy groups. upcoming large surveys will change this picture, reassigning to galaxy groups their central role in studying the structure formation and evolution in the universe, and in measuring the cosmic baryonic content. here, we review the recent literature on various scaling relations between x-ray and optical properties of these systems, focusing on the observational measurements, and the progress in our understanding of the deviations from the self-similar expectations on groups' scales. we discuss some of the sources of these deviations, and how feedback from supernovae and/or agns impacts the general properties and the reconstructed scaling laws. finally, we discuss future prospects in the study of galaxy groups. | scaling properties of galaxy groups |
we present the most extensive sample of 45 type i (short) and 275 type ii (long) gamma-ray bursts (grbs) with known redshift to investigate the correlation between the rest-frame peak energy, ep,i and the total isotropic equivalent energy, eiso of the prompt emission (amati relation). the ep,i-eiso correlation for type i bursts is found to be well distinguished from the one constructed for type ii bursts and has a similar power-law index value, ep,i∝ e_iso^{~0.4}, which possibly indicates the same emission mechanism of both grb types. we show that the initial pulse complex (ipc) of type i bursts with an extended emission and regular type i bursts follow the same correlation. we obtain similar results for type ii bursts associated with ic supernovae and for regular type ii bursts. three possible outliers from the ep,i-eiso correlation for type ii subsample are detected. significant evolution of the ep,i-eiso correlation with redshift for type ii bursts is not found. we suggest the new classification method, based on the ep,i-eiso correlation and introduce two parameters, eh = e_p,i,2 ~ e_iso,51^{~-0.4} and ehd = e_p,i,2 ~ e_iso,51^{~-0.4} ~ t_90,i^{~-0.5}, where ep,i,2 is the value of ep,i parameter in units of 100 kev, eiso,51 is the value of eiso parameter in units of 1051 erg, and t90,i is the rest-frame duration in units of seconds. ehd is found to be the most reliable parameter for the blind type i/type ii classification, which can be used to classify grbs with no redshift. | the ep,i-eiso correlation: type i gamma-ray bursts and the new classification method |
alma observations of z > 6 galaxies have revealed abnormally high [o iii]88 $\mu$m/[c ii]158 $\mu$m ratios and [c ii]158 $\mu$m deficits compared to local galaxies. the origin of this behaviour is unknown. numerous solutions have been proposed including differences in c and o abundance ratios, observational bias, and differences in ism properties, including ionization parameter, gas density, or photodissociation region (pdr) covering fraction. in order to elucidate the underlying physics that drives this high-redshift phenomenon, we employ sphinx20, a state-of-the-art, cosmological radiation-hydrodynamics simulation, that resolves detailed ism properties of thousands of galaxies in the epoch of reionization which has been post-processed with cloudy to predict emission lines. we find that the observed z > 6 [o iii]88 $\mu$m-sfr and [c ii]158 $\mu$m-sfr relations can only be reproduced when the c/o abundance ratio is ~8 × lower than solar and the total metal production is ~4 × higher than that of a kroupa imf. this implies that high-redshift galaxies are potentially primarily enriched by low-metallicity core-collapse supernovae with a more top-heavy imf. as agb stars and type-ia supernova begin to contribute to the galaxy metallicity, both the [c ii]158 $\mu$m-sfr and [c ii]158 $\mu$m luminosity functions are predicted to converge to observed values at z ~ 4.5. while we demonstrate that ionization parameter, lyc escape fraction, ism gas density, and cmb attenuation all drive galaxies towards higher [o iii]88 $\mu$m/[c ii]158 $\mu$m, observed values at z > 6 can only be reproduced with substantially lower c/o abundances compared to solar. the combination of [c ii]158 $\mu$m and [o iii]88 $\mu$m can be used to predict the values of ionization parameter, ism gas density, and lyc escape fraction and we provide estimates of these quantities for nine observed z > 6 galaxies. finally, we demonstrate that [o i]63 $\mu$m can be used as a replacement for [c ii]158 $\mu$ m in high-redshift galaxies where [c ii]158 $\mu$ m is unobserved and argue that more observation time should be used to target [o i]63 $\mu$m at z > 6. future simulations will be needed to self-consistently address the numerous uncertainties surrounding a varying imf at high redshift and the associated metal returns. | the nature of high [o iii]88 μ m/[c ii]158 μm galaxies in the epoch of reionization: low carbon abundance and a top-heavy imf? |
we introduce a generalized form of an emergent dark energy model with one degree of freedom for the dark energy sector that has the flexibility to include both the λcdm model as well as the phenomenologically emergent dark energy (pede) model proposed by li & shafieloo as two of its special limits. the free parameter for the dark energy sector, namely δ, has a value of 0 for the λ case and a value of 1 for the pede case. fitting the introduced parametric form to planck cosmic microwave background (cmb) data and recent h0 results from local observations of cepheids and supernovae, we show that the δ = 0 associated with the λcdm model would fall out of the 4&sgr; confidence limits of the derived posterior of the δ parameter. moreover, h0 tensions with the emergent dark energy model will be alleviated and this model can satisfy the combination of planck cmb data and local h0 observations with δdic = -2.88 compared with the λcdm model. | evidence for emergent dark energy |
measurements of the dark energy equation-of-state parameter, w, have been limited by uncertainty in the selection effects and photometric calibration of z < 0.1 type ia supernovae (sne ia). the foundation supernova survey is designed to lower these uncertainties by creating a new sample of z < 0.1 sne ia observed on the pan-starrs system. here we combine the foundation sample with sne from the pan-starrs medium deep survey and measure cosmological parameters with 1338 sne from a single telescope and a single, well-calibrated photometric system. for the first time, both the low-z and high-z data are predominantly discovered by surveys that do not target preselected galaxies, reducing selection bias uncertainties. the z > 0.1 data include 875 sne without spectroscopic classifications, and we show that we can robustly marginalize over cc sn contamination. we measure foundation hubble residuals to be fainter than the preexisting low-z hubble residuals by 0.046 ± 0.027 mag (stat + sys). by combining the sn ia data with cosmic microwave background constraints, we find w = -0.938 ± 0.053, consistent with λcdm. with 463 spectroscopically classified sne ia alone, we measure w = -0.933 ± 0.061. using the more homogeneous and better-characterized foundation sample gives a 55% reduction in the systematic uncertainty attributed to sn ia sample selection biases. although use of just a single photometric system at low and high redshift increases the impact of photometric calibration uncertainties in this analysis, previous low-z samples may have correlated calibration uncertainties that were neglected in past studies. the full foundation sample will observe up to 800 sne to anchor the lsst and wfirst hubble diagrams. | the foundation supernova survey: measuring cosmological parameters with supernovae from a single telescope |
cosmic microwave background (cmb) anisotropy (spatial inhomogeneity) data provide the tightest constraints on the hubble constant, matter density, spatial curvature, and dark energy dynamics. other data, sensitive to the evolution of only the spatially homogeneous part of the cosmological model, such as type ia supernova apparent magnitude, baryon acoustic oscillation distance, and hubble parameter measurements, can be used in conjunction with the cmb data to more tightly constrain parameters. recent joint analyses of cmb and such non-cmb data indicate that slightly closed spatial hypersurfaces are favored in nonflat untilted inflation models and that dark energy dynamics cannot be ruled out, and favor a smaller hubble constant. we show that the constraints that follow from these non-cmb data alone are consistent with those that follow from the cmb data alone and so also consistent with, but weaker than, those that follow from the joint analyses of the cmb and non-cmb data. | measuring the hubble constant and spatial curvature from supernova apparent magnitude, baryon acoustic oscillation, and hubble parameter data |
understanding ionizing fluxes of stellar populations is crucial for various astrophysical problems including the epoch of reionization. short-lived massive stars are generally considered as the main stellar sources. we examine the potential role of less massive stars that lose their envelope through interaction with a binary companion. here, we focus on the role of metallicity (z). for this purpose we used the evolutionary code mesa and created tailored atmosphere models with the radiative transfer code cmfgen. we show that typical progenitors, with initial masses of 12 m⊙, produce hot and compact stars ( 4 m⊙, 60-80 kk, 1 r⊙). these stripped stars copiously produce ionizing photons, emitting 60-85% and 30-60% of their energy as hi and hei ionizing radiation, for z = 0.0001-0.02, respectively. their output is comparable to what massive stars emit during their wolf-rayet phase, if we account for their longer lifetimes and the favorable slope of the initial mass function. their relative importance for reionization may be further favored since they emit their photons with a time delay ( 20 myr after birth in our fiducial model). this allows time for the dispersal of the birth clouds, allowing the ionizing photons to escape into the intergalactic medium. at low z, we find that roche stripping fails to fully remove the h-rich envelope, because of the reduced opacity in the subsurface layers. this is in sharp contrast with the assumption of complete stripping that is made in rapid population synthesis simulations, which are widely used to simulate the binary progenitors of supernovae and gravitational waves. finally, we discuss the urgency to increase the observed sample of stripped stars to test these models and we discuss how our predictions can help to design efficient observational campaigns. | ionizing spectra of stars that lose their envelope through interaction with a binary companion: role of metallicity |
the cumulative emission of axionlike particles (alps) from all past core-collapse supernovae (sne) would lead to a diffuse flux with energies o (50 ) mev . we use this to constrain alps featuring couplings to photons and to nucleons. alps coupled only to photons are produced in the sn core via the primakoff process and then converted into gamma rays in the galactic magnetic field. we set a bound on ga γ≲5 ×10-10 gev-1 for ma≲10-11 ev , using recent measurements of the diffuse gamma-ray flux observed by the fermi-lat telescope. however, if alps couple also with nucleons, their production rate in sn can be considerably enhanced due to the alps nucleon-nucleon bremsstrahlung process. assuming the largest alp-nucleon coupling phenomenologically allowed, bounds on the diffuse gamma-ray flux lead to a much stronger ga γ≲6 ×10-13 gev-1 for the same mass range. if alps are heavier than ∼kev , the decay into photons becomes significant, leading again to a diffuse gamma-ray flux. in the case of only photon coupling, we find, e.g., ga γ≲5 ×10-11 gev-1 for ma∼5 kev . allowing for a (maximal) coupling to nucleons, the limit improves to the level of ga γ≲10-19 gev-1 for ma∼20 mev , which represents the strongest constraint to date. | bounds on axionlike particles from the diffuse supernova flux |
we present a determination of the hubble constant from the joint, free-form analysis of eight strongly, quadruply lensing systems. in the concordance cosmology, we find $h_0{} = 71.8^{+3.9}_{-3.3}\, \mathrm{km}\, \mathrm{s}^{-1}\, \mathrm{mpc}^{-1}{}{}$ with a precision of $4.97{{\ \rm per\ cent}}$. this is in agreement with the latest measurements from supernovae type ia and planck observations of the cosmic microwave background. our precision is lower compared to these and other recent time-delay cosmography determinations, because our modelling strategies reflect the systematic uncertainties of lensing degeneracies. we furthermore are able to find reasonable lensed image reconstructions by constraining to either value of h0 from local and early universe measurements. this leads us to conclude that current lensing constraints on h0 are not strong enough to break the 'hubble tension' problem of cosmology. | the hubble constant from eight time-delay galaxy lenses |
type ii supernovae (sne ii) originate from the explosion of hydrogen-rich supergiant massive stars. their first electromagnetic signature is the shock breakout (sbo), a short-lived phenomenon that can last for hours to days depending on the density at shock emergence. we present 26 rising optical light curves of sn ii candidates discovered shortly after explosion by the high cadence transient survey and derive physical parameters based on hydrodynamical models using a bayesian approach. we observe a steep rise of a few days in 24 out of 26 sn ii candidates, indicating the systematic detection of sbos in a dense circumstellar matter consistent with a mass loss rate of m ˙ > 10-4m⊙ yr-1 or a dense atmosphere. this implies that the characteristic hour-timescale signature of stellar envelope sbos may be rare in nature and could be delayed into longer-lived circumstellar material sbos in most sne ii. | the delay of shock breakout due to circumstellar material evident in most type ii supernovae |
chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. however, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (sfe), the stellar initial mass function, the sn ia delay time distribution, stellar yields, and stellar population mixing. using flexce, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. two critical parameters are sfe and the outflow mass-loading parameter, which shift the knee in [o/fe]-[fe/h] and the equilibrium abundances that the simulations asymptotically approach, respectively. one-zone models with simple star formation histories follow narrow tracks in [o/fe]-[fe/h] unlike the observed bimodality (separate high-α and low-α sequences) in this plane. a mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. we present [x/fe]-[fe/h] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. we apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. for the stellar population mixing scenario, the abundances of α-elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexce is a python package available at https://github.com/bretthandrews/flexce. | inflow, outflow, yields, and stellar population mixing in chemical evolution models |
gravitational wave transients, resulting from the merger of two stellar remnants, are now detectable. the properties and rates of these directly relates to the stellar population which gave rise to their progenitors, and thus to other electromagnetic transients which result from stellar death. we aim to estimate simultaneously the event rates and delay-time distribution of gravitational wave-driven compact object mergers together with the rates of core collapse and thermonuclear supernovae within a single consistent stellar population synthesis paradigm. we combine event delay-time distributions at different metallicities from the binary population and spectral synthesis models with an analytic model of the volume-averaged cosmic star formation rate density and chemical evolution to determine the volume-averaged rates of each event rate at the current time. we estimate rates in excellent agreement with extant observational constraints on core-collapse supernovae, thermonuclear supernovae, and long gamma-ray bursts. we predict rates for gravitational wave mergers based on the same stellar populations, and find rates consistent with current ligo estimates. we note that tighter constraints on the rates of these events will be required before it is possible to determine their redshift evolution, progenitor metallicity dependence, or constrain uncertain aspects of stellar evolution. | a consistent estimate for gravitational wave and electromagnetic transient rates |
type ia supernovae arise from the thermonuclear explosion of white-dwarf stars that have cores of carbon and oxygen. the uniformity of their light curves makes these supernovae powerful cosmological distance indicators, but there have long been debates about exactly how their explosion is triggered and what kind of companion stars are involved. for example, the recent detection of the early ultraviolet pulse of a peculiar, subluminous type ia supernova has been claimed as evidence for an interaction between a red-giant or a main-sequence companion and ejecta from a white-dwarf explosion. here we report observations of a prominent but red optical flash that appears about half a day after the explosion of a type ia supernova. this supernova shows hybrid features of different supernova subclasses, namely a light curve that is typical of normal-brightness supernovae, but with strong titanium absorption, which is commonly seen in the spectra of subluminous ones. we argue that this early flash does not occur through previously suggested mechanisms such as the companion-ejecta interaction. instead, our simulations show that it could occur through detonation of a thin helium shell either on a near-chandrasekhar-mass white dwarf, or on a sub-chandrasekhar-mass white dwarf merging with a less-massive white dwarf. our finding provides evidence that one branch of previously proposed explosion models—the helium-ignition branch—does exist in nature, and that such a model may account for the explosions of white dwarfs in a mass range wider than previously supposed. | a hybrid type ia supernova with an early flash triggered by helium-shell detonation |
extreme stripped-envelope supernovae (sesne), including type ic superluminous supernovae (slsne), broad-line type ic sne (sne ic-bl), and fast blue optical transients (fbots), are widely believed to harbor a newborn fast-spinning highly-magnetized neutron star (``magnetar''), which can lose its rotational energy via spin-down processes to accelerate and heat the ejecta. the progenitor(s) of these magnetar-driven sesne, and the origin of considerable angular momentum (am) in the cores of massive stars to finally produce such fast-spinning magnetars upon core-collapse are still under debate. popular proposed scenarios in the literature cannot simultaneously explain their event rate density, sn and magnetar parameters, and the observed metallicity. here, we perform a detailed binary evolution simulation that demonstrates that tidal spin-up helium stars with efficient am transport mechanism in close binaries can form fast-spinning magnetars at the end of stars' life to naturally reproduce the universal energy-mass correlation of these magnetar-driven sesne. our models are consistent with the event rate densities, host environments, ejecta masses, and energetics of these different kinds of magnetar-driven sesne, supporting that the isolated common-envelope formation channel could be a major common origin of magnetar-driven sesne. the remnant compact binary systems of magnetar-driven sesne are progenitors of some galactic systems and gravitational-wave transients. | formation of fast-spinning neutron stars in close binaries and magnetar-driven stripped-envelope supernovae |
the importance of detecting neutrinos from a milky way core-collapse supernova is well known. an understudied phase is proto-neutron star cooling. for sn 1987a, this seemingly began at about 2 s and is thus probed by only 6 of the 19 events (and only the ν¯e flavor) in the kamiokande-ii and imb detectors. with the higher statistics expected for present and near-future detectors, it should be possible to measure detailed neutrino signals out to very late times. we present the first comprehensive study of neutrino detection during the proto-neutron star cooling phase, considering a variety of outcomes, using all flavors, and employing detailed detector physics. for our nominal model, the event yields (at 10 kpc) after 10 s—the approximate duration of the sn 1987a signal—far exceed the entire sn 1987a yield, with ≃250 ν¯e events (to 50 s) in super-kamiokande, ≃110 νe events (40 s) in the deep underground neutrino experiment (dune), and ≃10 νμ,ντ,ν¯μ,ν¯τ events (to 20 s) in the jiangmen underground neutrino observatory. these data would allow unprecedented probes of the proto-neutron star, including the onset of neutrino transparency and hence its transition to a neutron star. if a black hole forms, even at very late times, this can be clearly identified. but will the detectors fulfill their potential for this perhaps once-ever opportunity for an all-flavor, high-statistics detection of a core collapse? maybe. further work is urgently needed, especially for dune to thoroughly investigate and improve its mev capabilities. | exciting prospects for detecting late-time neutrinos from core-collapse supernovae |
based on our recent three-dimensional core-collapse supernova (ccsn) simulations including both exploding and non-exploding models, we study the detailed neutrino signals in representative terrestrial neutrino observatories, namely super-kamiokande (hyper-kamiokande), dune, juno, and icecube. we find that the physical origin of difference in the neutrino signals between 1d and 3d is mainly proto-neutron-star convection. we study the temporal and angular variations of the neutrino signals and discuss the detectability of the time variations driven by the spiral standing accretion shock instability (spiral sasi) when it emerges for non-exploding models. in addition, we determine that there can be a large angular asymmetry in the event rate (${\gtrsim} 50 {{\ \rm per\ cent}}$), but the time-integrated signal has a relatively modest asymmetry (${\lesssim} 20 {{\ \rm per\ cent}}$). both features are associated with the lepton-number emission self-sustained asymmetry and the spiral sasi. moreover, our analysis suggests that there is an interesting correlation between the total neutrino energy (tone) and the cumulative number of neutrino events in each detector, a correlation that can facilitate data analyses of real observations. we demonstrate the retrieval of neutrino energy spectra for all flavours of neutrino by applying a novel spectrum reconstruction technique to the data from multiple detectors. we find that this new method is capable of estimating the tone within the error of ~20 per cent if the distance to the ccsn is ≲6 kpc. | core-collapse supernova neutrino emission and detection informed by state-of-the-art three-dimensional numerical models |
we analyze new jwst nircam and nirspec data on the redshift 9.11 galaxy macs1149-jd1 (hereafter jd1). our nircam imaging data reveal that jd1 comprises three spatially distinct components. our spectroscopic data indicate that jd1 appears dust free but is already enriched, $12+\mathrm{log}({\rm{o}}/{\rm{h}})={7.90}_{-0.05}^{+0.04}$ . we also find that the carbon and neon abundances in jd1 are below the solar abundance ratio. particularly the carbon under-abundance is suggestive of recent star formation where type ii supernovae have already enriched the interstellar medium (ism) in oxygen but intermediate mass stars have not yet enriched the ism in carbon. a recent burst of star formation is also revealed by the star formation history derived from nircam photometry. our data do not reveal the presence of a significant amount of old populations, resulting in a factor of ~7× smaller stellar mass than previous estimates. thus, our data support the view that jd1 is a young galaxy. | the puzzling properties of the macs1149-jd1 galaxy at z = 9.11 |
we construct evolutionary models of the remnant of the merger of two carbon-oxygen (co) core white dwarfs (wds). with total masses in the range 1-2 m⊙, these remnants may either leave behind a single massive wd or undergo a merger-induced collapse to a neutron star (ns). on the way to their final fate, these objects generally experience a ∼10 kyr luminous giant phase, which may be extended if sufficient helium remains to set up a stable shell-burning configuration. the uncertain, but likely significant, mass-loss rate during this phase influences the final remnant mass and fate (wd or ns). we find that the initial co core composition of the wd is converted to oxygen-neon (one) in remnants with final masses ≳1.05 m⊙. this implies that the co core/one core transition in single wds formed via mergers occurs at a similar mass as in wds descended from single stars and thus that wd-wd mergers do not naturally provide a route to producing ultramassive co-core wds. as the remnant contracts toward a compact configuration, it experiences a "bottleneck" that sets the characteristic total angular momentum that can be retained. this limit predicts that single wds formed from wd-wd mergers have rotational periods of ≈10-20 minutes on the wd cooling track. similarly, it predicts remnants that collapse can form nss with rotational periods ∼10 ms. | evolutionary models for the remnant of the merger of two carbon-oxygen core white dwarfs |
the star formation rate (sfr) in galactic disks depends on both the quantity of the available interstellar medium (ism) gas and its physical state. conversely, the ism's physical state depends on the sfr, because the "feedback" energy and momentum injected by recently formed massive stars is crucial to offsetting losses from turbulent dissipation and radiative cooling. the ism's physical state also responds to the gravitational field that confines it, with increased weight driving higher pressure. in a quasi-steady state, it is expected that the mean total pressure of different thermal phases will match each other, that the component pressures and total pressure will satisfy thermal and dynamical equilibrium requirements, and that the sfr will adjust as needed to provide the requisite stellar radiation and supernova feedback. the pressure-regulated, feedback-modulated (prfm) theory of the star-forming ism formalizes these ideas, leading to a prediction that the sfr per unit area, σsfr, will scale nearly linearly with ism weight ${ \mathcal w }$ . in terms of the large-scale gas surface density σgas, stellar plus dark matter density ρ sd, and effective ism velocity dispersion σ eff, an observable weight estimator is ${ \mathcal w }\approx {p}_{\mathrm{de}}=\pi g{{\rm{\sigma }}}_{\mathrm{gas}}^{2}/2+{{\rm{\sigma }}}_{\mathrm{gas}}{(2g{\rho }_{\mathrm{sd}})}^{1/2}{\sigma }_{\mathrm{eff}}$ , and this is predicted to match the total midplane pressure p tot. using a suite of multiphase magnetohydrodynamic simulations run with the tigress computational framework, we test the principles of the prfm model and calibrate the total feedback yield ϒtot = p tot/σsfr ~ 1000 km s-1, as well as its components. we compare the results from tigress to theory, previous numerical simulations, and observations, finding excellent agreement. | pressure-regulated, feedback-modulated star formation in disk galaxies |
we introduce a semiparametric model for the primary mass distribution of binary black holes (bbhs) observed with gravitational waves (gws) that applies a cubic-spline perturbation to a power law. we apply this model to the 46 bbhs included in the second gravitational-wave transient catalog (gwtc-2). the spline perturbation model recovers a consistent primary mass distribution with previous results, corroborating the existence of a peak at 35 m ⊙ (>97% credibility) found with the powerlaw+peak model. the peak could be the result of pulsational pair-instability supernovae. the spline perturbation model finds potential signs of additional features in the primary mass distribution at lower masses similar to those previously reported by tiwari and fairhurst. however, with fluctuations due to small-number statistics, the simpler powerlaw+peak and brokenpowerlaw models are both still perfectly consistent with observations. our semiparametric approach serves as a way to bridge the gap between parametric and nonparametric models to more accurately measure the bbh mass distribution. with larger catalogs we will be able to use this model to resolve possible additional features that could be used to perform cosmological measurements and will build on our understanding of bbh formation, stellar evolution, and nuclear astrophysics. | ain't no mountain high enough: semiparametric modeling of ligo-virgo's binary black hole mass distribution |
cosmological probes at any redshift are necessary to reconstruct consistently the cosmic history. studying properly the tension on the hubble constant, h0, obtained by supernovae type ia (sne ia) and the planck measurements of the cosmic microwave background radiation would require complete samples of distance indicators at any epoch. gamma-ray bursts (grbs) are necessary for the aforementioned task because of their huge luminosity that allows us to extend the cosmic ladder to very high redshifts. however, using grbs alone as standard candles is challenging, because their luminosity varies widely. to this end, we choose a reliable correlation for grbs with a very small intrinsic scatter: the so-called fundamental plane correlation for grb afterglows corrected for selection biases and redshift evolution. we choose a well defined sample: the platinum sample, composed of 50 long grbs. to further constrain the cosmological parameters, we use baryon acoustic oscillations (baos) given their reliability as standard rulers. thus, we have applied grbs, sne ia, and baos in a binned analysis in redshifts so that the grb contribution is fully included in the last redshift bin, which reaches z = 5. we use the fundamental plane correlation (also known as the 3d dainotti relation), together with sne ia and baos, to constrain h0 and the density matter today, ωm. this methodology allows us to assess the role of grbs combined with sne ia and baos. we have obtained results for h0 and ωm using grbs+sne ia+baos with better precision than sne ia alone for every bin, thus confirming the beneficial role of baos and grbs added together. in addition, consistent results between grbs+sne ia+baos are obtained when compared with sne ia+baos, showing the importance of grbs since the distance ladder is extended up to z = 5 with a similar precision obtained with other probes without including grbs. | gamma-ray bursts, supernovae ia, and baryon acoustic oscillations: a binned cosmological analysis |
we discuss as accurately as possible the cross section of quasi-elastic scattering of electron (anti-)neutrinos on nucleons, also known as inverse beta decay in the case of antineutrinos. we focus on the moderate energy range from a few mev up to hundreds of mev, which includes neutrinos from reactors and supernovae. we assess the uncertainty on the cross section, which is relevant to experimental advances and increasingly large statistical samples. we estimate the effects of second-class currents, showing that they are small and negligible for current applications. | an accurate evaluation of electron (anti-)neutrino scattering on nucleons |
some cosmological models with non-negligible dark energy fractions, in particular windows of the prerecombination epoch, are capable of alleviating the hubble tension quite efficiently, while keeping the good description of the data that are used to build the cosmic inverse distance ladder. there has been an intensive discussion in the community on whether these models enhance the power of matter fluctuations, leading de facto to a worsening of the tension with the large-scale structure measurements. we address this pivotal question in the context of several early dark energy (ede) models, considering also in some cases a coupling between dark energy and dark matter, and the effect of massive neutrinos. we fit them using the planck 2018 likelihoods, the supernovae of type ia from the pantheon compilation, and data on baryon acoustic oscillations. we find that ultralight axion-like (ula) ede can actually alleviate the h0 tension without increasing the values of σ12 with respect to those found in the λ cdm , whereas ede with an exponential potential does not have any impact on the tensions. a coupling in the dark sector tends to enhance the clustering of matter, and the data limit greatly the influence of massive neutrinos, since the upper bounds on the sum of their masses are too close to those obtained in the standard model. we find that in the best case, namely ula, the hubble tension is reduced to ∼2 σ . | coupled and uncoupled early dark energy, massive neutrinos, and the cosmological tensions |
core-collapse supernovae (ccsne) are prime candidates for gravitational-wave detectors. the analysis of their complex waveforms can potentially provide information on the physical processes operating during the collapse of the iron cores of massive stars. in this work we analyze the early-bounce rapidly rotating ccsn signals reported in the waveform catalog of richers et al 2017, which comprises over 1800 axisymmetric simulations extending up to about $10$~ms of post-bounce evolution. it was previously established that for a large range of progenitors, the amplitude of the bounce signal, $\delta h$, is proportional to the ratio of rotational-kinetic energy to potential energy, t/|w|, and the peak frequency, $f_{\rm peak}$, is proportional to the square root of the central rest-mass density. in this work, we exploit these relations to suggest that it could be possible to use such waveforms to infer protoneutron star properties from a future gravitational wave observation, if the distance and inclination are well known. our approach relies on the ability to describe a subset of the waveforms in the early post-bounce phase in a simple template form depending only on two parameters, $\delta h$ and $f_{\rm peak}$. we use this template to perform a bayesian inference analysis of waveform injections in gaussian colored noise for a network of three gravitational wave detectors formed by advanced ligo and advanced virgo. we show that it is possible to recover the injected parameters, peak frequency and amplitude, with an accuracy better than 10% for more than 50% of the detectable signals (given known distance and inclination angle). however, inference on waveforms from outside the richers catalog is not reliable, indicating a need for carefully verified waveforms of the first 10 ms after bounce of rapidly rotating supernovae of different progenitors with agreement between different codes. | bayesian inference from gravitational waves in fast-rotating, core-collapse supernovae |
fulfilling the rich promise of rapid advances in time-domain astronomy is only possible through confronting our observations with physical models and extracting the parameters that best describe what we see. here, we introduce {\sc redback}; a bayesian inference software package for electromagnetic transients. {\sc redback} provides an object-orientated {\sc python} interface to over 12 different samplers and over 100 different models for kilonovae, supernovae, gamma-ray burst afterglows, tidal disruption events, engine-driven transients, x-ray afterglows of gamma-ray bursts driven by millisecond magnetars among other explosive transients. the models range in complexity from simple analytical and semi-analytical models to surrogates built upon numerical simulations accelerated via machine learning. {\sc redback} also provides a simple interface for downloading and processing data from swift, fink, lasair, the open-access catalogues, and batse and fit this or private data. {\sc redback} can also be used as an engine to simulate transients for telescopes such as the zwicky transient facility and vera rubin with realistic cadences, limiting magnitudes, and sky-coverage or a hypothetical user-constructed survey with arbitrary settings. we also provide a more general simulation interface suitable for target of opportunity observations with different telescopes. we demonstrate through a series of examples how {\sc redback} can be used as a tool to simulate a large population of transients for realistic surveys, fit models to real, simulated, or private data, multi-messenger inference and serve as an end-to-end software toolkit for parameter estimation and interpreting the nature of electromagnetic transients. | redback: a bayesian inference software package for electromagnetic transients |
we re-examine the classifications of supernovae (sne) presented in the lick observatory supernova search (loss) volume-limited sample with a focus on the stripped-envelope sne. the loss volume-limited sample, presented by leaman et al. and li et al., was calibrated to provide meaningful measurements of sn rates in the local universe; the results presented therein continue to be used for comparisons to theoretical and modeling efforts. many of the objects from the loss sample were originally classified based upon only a small subset of the data now available, however, and recent studies have both updated some subtype distinctions and improved our ability to perform robust classifications, especially for stripped-envelope sne. we re-examine the spectroscopic classifications of all events in the loss volume-limited sample (180 sne and sn impostors) and update them if necessary. we discuss the populations of rare objects in our sample including broad-lined sne ic, ca-rich sne, sn 1987a-like events (we identify sn 2005io as sn 1987a-like here for the first time), and peculiar subtypes. the relative fractions of sne ia, sne ii, and stripped-envelope sne in the local universe are not affected, but those of some subtypes are. most significantly, after discussing the often unclear boundary between sne ib and ic when only noisy spectra are available, we find a higher sn ib fraction and a lower sn ic fraction than calculated by li et al.: spectroscopically normal sne ib occur in the local universe 1.7 ± 0.9 times more often than do normal sne ic. | revisiting the lick observatory supernova search volume-limited sample: updated classifications and revised stripped-envelope supernova fractions |
non-thermal particles and high-energy radiation can play a role in the dynamical processes in star-forming regions and provide an important piece of the multiwavelength observational picture of their structure and components. powerful stellar winds and supernovae in compact clusters of massive stars and ob associations are known to be favourable sites of high-energy particle acceleration and sources of non-thermal radiation and neutrinos. namely, young massive stellar clusters are likely sources of the pev (petaelectronvolt) regime cosmic rays (crs). they can also be responsible for the cosmic ray composition, e.g., 22ne/20ne anomalous isotopic ratio in crs. efficient particle acceleration can be accompanied by super-adiabatic amplification of the fluctuating magnetic fields in the systems converting a part of kinetic power of the winds and supernovae into the magnetic energy through the cr-driven instabilities. the escape and cr propagation in the vicinity of the sources are affected by the non-linear cr feedback. these effects are expected to be important in starburst galaxies, which produce high-energy neutrinos and gamma-rays. we give a brief review of the theoretical models and observational data on high-energy particle acceleration and their radiation in star-forming regions with young stellar population. | high-energy particles and radiation in star-forming regions |
ions produced by cosmic rays have been thought to influence aerosols and clouds. in this study, the effect of ionization on the growth of aerosols into cloud condensation nuclei is investigated theoretically and experimentally. we show that the mass-flux of small ions can constitute an important addition to the growth caused by condensation of neutral molecules. under atmospheric conditions the growth from ions can constitute several percent of the neutral growth. we performed experimental studies which quantify the effect of ions on the growth of aerosols between nucleation and sizes >20 nm and find good agreement with theory. ion-induced condensation should be of importance not just in earth's present day atmosphere for the growth of aerosols into cloud condensation nuclei under pristine marine conditions, but also under elevated atmospheric ionization caused by increased supernova activity. | increased ionization supports growth of aerosols into cloud condensation nuclei |
the tin sulfides sns, sn2s3 , and sn s2 are investigated for a wide variety of applications such as photovoltaics, thermoelectrics, two-dimensional electronic devices, li ion battery electrodes, and photocatalysts. for these applications, native point defects play important roles, but only those of sns have been investigated theoretically in the literature. in this study, we consider the band structures, band-edge positions, and thermodynamical stability of the tin sulfides using a density functional that accounts for van der waals corrections and the g w0 approximation. we revisit the point-defect properties, namely, electronic and atomic structures and energetics of defects, in sns and newly examine those in sn s2 and sn2s3 with a comparison to those in sns. we find that sn s2 shows contrasting defect properties to sns: undoped sns shows p -type behavior, whereas sn s2 shows n type, which are mainly attributed to the tin vacancies and tin interstitials, respectively. we also find that the defect features in sn2s3 can be described as a combination of those in sns and sn s2 , intrinsically sn2s3 showing n -type behavior. however, the conversion to p type can be attained by doping with a large monovalent cation, namely, potassium. the ambipolar dopability, coupled with the earth abundance of its constituents, indicates great potential for electronic applications, including photovoltaics. | electronic structure and defect physics of tin sulfides: sns, sn2s3 , and sn s2 |
the most direct and strongest evidence for the presence of dark energy is provided by the measurement of galaxy distances using sne ia. this result is based on the assumption that the corrected brightness of sn ia through the empirical standardization would not evolve with look-back time. recent studies have shown, however, that the standardized brightness of sn ia is correlated with host morphology, host mass, and local star formation rate (sfr), suggesting a possible correlation with stellar population property. to understand the origin of these correlations, we have continued our spectroscopic observations to cover most of the reported nearby early-type host galaxies. from high-quality (signal-to-noise ratio ∼175) spectra, we obtained the most direct and reliable estimates of population age and metallicity for these host galaxies. we find a significant correlation between sn luminosity (after the standardization) and stellar population age at a 99.5% confidence level. as such, this is the most direct and stringent test ever made for the luminosity evolution of sn ia. based on this result, we further show that the previously reported correlations with host morphology, host mass, and local sfr are most likely originated from the difference in population age. this indicates that the light-curve fitters used by the sne ia community are not quite capable of correcting for the population age effect, which would inevitably cause a serious systematic bias with look-back time. notably, taken at face values, most of the hubble residual used in the discovery of the dark energy appears to be affected by the luminosity evolution. | early-type host galaxies of type ia supernovae. ii. evidence for luminosity evolution in supernova cosmology |
we summarize our current understanding of gravitational wave emission from core-collapse supernovae. we review the established results from multi-dimensional simulations and, wherever possible, provide back-of-the-envelope calculations to highlight the underlying physical principles. the gravitational waves are predominantly emitted by protoneutron star oscillations. in slowly rotating cases, which represent the most common type of the supernovae, the oscillations are excited by multi-dimensional hydrodynamic instabilities, while in rare rapidly rotating cases, the protoneutron star is born with an oblate deformation due to the centrifugal force. the gravitational wave signal may be marginally visible with current detectors for a source within our galaxy, while future third-generation instruments will enable more robust and detailed observations. the rapidly rotating models that develop non-axisymmetric instabilities may be visible up to a megaparsec distance with the third-generation detectors. finally, we discuss strategies for multi-messenger observations of supernovae. | gravitational waves from core-collapse supernovae |
we present a systematic search for wide-separation (with einstein radius θe ≳ 1.5″), galaxy-scale strong lenses in the 30 000 deg2 of the pan-starrs 3π survey on the northern sky. with long time delays of a few days to weeks, these types of systems are particularly well-suited for catching strongly lensed supernovae with spatially-resolved multiple images and offer new insights on early-phase supernova spectroscopy and cosmography. we produced a set of realistic simulations by painting lensed cosmos sources on pan-starrs image cutouts of lens luminous red galaxies (lrgs) with redshift and velocity dispersion known from the sloan digital sky survey (sdss). first, we computed the photometry of mock lenses in gri bands and applied a simple catalog-level neural network to identify a sample of 1 050 207 galaxies with similar colors and magnitudes as the mocks. second, we trained a convolutional neural network (cnn) on pan-starrs gri image cutouts to classify this sample and obtain sets of 105 760 and 12 382 lens candidates with scores of pcnn > 0.5 and > 0.9, respectively. extensive tests showed that cnn performances rely heavily on the design of lens simulations and the choice of negative examples for training, but little on the network architecture. the cnn correctly classified 14 out of 16 test lenses, which are previously confirmed lens systems above the detection limit of pan-starrs. finally, we visually inspected all galaxies with pcnn > 0.9 to assemble a final set of 330 high-quality newly-discovered lens candidates while recovering 23 published systems. for a subset, sdss spectroscopy on the lens central regions proves that our method correctly identifies lens lrgs at z ∼ 0.1-0.7. five spectra also show robust signatures of high-redshift background sources, and pan-starrs imaging confirms one of them as a quadruply-imaged red source at zs = 1.185, which is likely a recently quenched galaxy strongly lensed by a foreground lrg at zd = 0.3155. in the future, high-resolution imaging and spectroscopic follow-up will be required to validate pan-starrs lens candidates and derive strong lensing models. we also expect that the efficient and automated two-step classification method presented in this paper will be applicable to the ∼4 mag deeper gri stacks from the rubin observatory legacy survey of space and time (lsst) with minor adjustments. full table 1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/644/a163 | holismokes. ii. identifying galaxy-scale strong gravitational lenses in pan-starrs using convolutional neural networks |
we find that models of mev-gev dark matter in which dark matter interacts strongly can be constrained by the observation of gravitational waves from binary neutron star (bns) mergers. trace amounts of dark matter, either produced during the supernova or accreted later, can alter the structure of neutron stars (ns) and influence their tidal deformability. we focus on models of dark matter interacting by the exchange of light vector gauge bosons that couple to a conserved dark charge. in these models, dark matter accumulated in neutron stars can extend to large radii. gravitational waves detected from the first observed bns merger gw170817 places useful constraints on such not-so compact objects. dark halos, if present, also predict a greater variability of neutron star tidal deformabilities than expected for ordinary neutron stars. | dark halos around neutron stars and gravitational waves |
for the origin of heavy rapid neutron capture process (r-process) elements, different sources have been proposed, e.g. core-collapse supernovae or neutron star mergers. old metal-poor stars carry the signature of the astrophysical source(s). among the elements dominantly made by the r-process, europium (eu) is relatively easy to observe. in this work we simulate the evolution of eu in our galaxy with the inhomogeneous chemical evolution (ice) model, and compare our results with spectroscopic observations. we test the most important parameters affecting the chemical evolution of eu: (a) for neutron star mergers the coalescence time-scale of the merger (tcoal) and the probability to experience a neutron star merger event after two supernova explosions occurred and formed a double neutron star system (pnsm) and (b) for the subclass of magnetorotationally driven supernovae (`jet-sne'), their occurrence rate compared to standard supernovae (pjet-sn). we find that the observed [eu/fe] pattern in the galaxy can be reproduced by a combination of neutron star mergers and jet-sne as r-process sources. while neutron star mergers alone seem to set in at too high metallicities, jet-sne provide a cure for this deficiency at low metallicities. furthermore, we confirm that local inhomogeneities can explain the observed large spread in the eu abundances at low metallicities. we also predict the evolution of [o/fe] to test whether the spread in α-elements for inhomogeneous models agrees with observations and whether this provides constraints on supernova explosion models and their nucleosynthesis. | galactic evolution of rapid neutron capture process abundances: the inhomogeneous approach |
we present optical and near-infrared (nir, y-, j-, h-band) observations of 42 type ia supernovae (sne ia) discovered by the untargeted intermediate palomar transient factory survey. this new data set covers a broad range of redshifts and host galaxy stellar masses, compared to previous sn ia efforts in the nir. we construct a sample, using also literature data at optical and nir wavelengths, to examine claimed correlations between the host stellar masses and the hubble diagram residuals. the sn magnitudes are corrected for host galaxy extinction using either a global total-to-selective extinction ratio, rv= 2.0, for all sne, or a best-fit rvfor each sn individually. unlike previous studies that were based on a narrower range in host stellar mass, we do not find evidence for a "mass step," between the color- and stretch-corrected peak j and h magnitudes for galaxies below and above $\mathrm{log}({m}_{* }/{m}_{\odot })=10$ . however, the mass step remains significant (3σ) at optical wavelengths (g, r, i) when using a global rv , but vanishes when each sn is corrected using their individual best-fit rv . our study confirms the benefits of the nir sn ia distance estimates, as these are largely exempted from the empirical corrections dominating the systematic uncertainties in the optical. | near-infrared supernova ia distances: host galaxy extinction and mass-step corrections revisited |
the limits of standard cosmography are here revised addressing the problem of error propagation during statistical analyses. to do so, we propose the use of chebyshev polynomials to parametrize cosmic distances. in particular, we demonstrate that building up rational chebyshev polynomials significantly reduces error propagations with respect to standard taylor series. this technique provides unbiased estimations of the cosmographic parameters and performs significatively better than previous numerical approximations. to figure this out, we compare rational chebyshev polynomials with padé series. in addition, we theoretically evaluate the convergence radius of (1,1) chebyshev rational polynomial and we compare it with the convergence radii of taylor and padé approximations. we thus focus on regions in which convergence of chebyshev rational functions is better than standard approaches. with this recipe, as high-redshift data are employed, rational chebyshev polynomials remain highly stable and enable one to derive highly accurate analytical approximations of hubble's rate in terms of the cosmographic series. finally, we check our theoretical predictions by setting bounds on cosmographic parameters through monte carlo integration techniques, based on the metropolis-hastings algorithm. we apply our technique to high-redshift cosmic data, using the joint light-curve analysis supernovae sample and the most recent versions of hubble parameter and baryon acoustic oscillation measurements. we find that cosmography with taylor series fails to be predictive with the aforementioned data sets, while turns out to be much more stable using the chebyshev approach. | cosmographic analysis with chebyshev polynomials |
core-collapse supernovae are among the most magnificent events in the observable universe. they produce many of the chemical elements necessary for life to exist and their remnants-neutron stars and black holes-are interesting astrophysical objects in their own right. however, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. hyper-kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. we focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate hyper-kamiokande's response to five different supernova models. we show that hyper-kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations toward a precise reproduction of the explosion mechanism observed in nature. | supernova model discrimination with hyper-kamiokande |
the ultra-faint dwarf (ufd) galaxy reticulum 2 (ret 2) was recently discovered in images obtained by the dark energy survey. we have observed the four brightest red giants in ret 2 at high spectral resolution using the michigan/magellan fiber system. we present detailed abundances for as many as 20 elements per star, including 12 elements heavier than the fe group. we confirm previous detection of high levels of r-process material in ret 2 (mean [eu/fe] = +1.69 ± 0.05) found in three of these stars (mean [fe/h] = -2.88 ± 0.10). the abundances closely match the r-process pattern found in the well-studied metal-poor halo star cs 22892-052. such r-process-enhanced stars have not been found in any other ufd galaxy, though their existence has been predicted by at least one model. the fourth star in ret 2 ([fe/h] = -3.42 ± 0.20) contains only trace amounts of sr ([sr/fe] = -1.73 ± 0.43) and no detectable heavier elements. one r-process enhanced star is also enhanced in c (natal [c/fe] ≈ +1.1). this is only the third such star known, which suggests that the nucleosynthesis sites leading to c and r-process enhancements are decoupled. the r-process-deficient star is enhanced in mg ([mg/fe] = +0.81 ± 0.14), and the other three stars show normal levels of α-enhancement (mean [mg/fe] = +0.34 ± 0.03). the abundances of other α and fe-group elements closely resemble those in ufd galaxies and metal-poor halo stars, suggesting that the nucleosynthesis that led to the large r-process enhancements either produced no light elements or produced light-element abundance signatures indistinguishable from normal supernovae. this paper includes data gathered with the 6.5 m magellan telescopes located at las campanas observatory, chile. | detailed chemical abundances in the r-process-rich ultra-faint dwarf galaxy reticulum 2 |
there are a growing number of nearby supernovae (sne) for which the progenitor star is detected in archival pre-explosion imaging. from these images it is possible to measure the progenitor's brightness a few years before explosion, and ultimately estimate its initial mass. previous work has shown that ii-p and ii-l sne have red supergiant (rsg) progenitors, and that the range of initial masses for these progenitors seems to be limited to ≲ 17 m⊙. this is in contrast with the cut-off of 25-30 m⊙ predicted by evolutionary models, a result that is termed the `red supergiant problem'. here we investigate one particular source of systematic error present in converting pre-explosion photometry into an initial mass, which of the bolometric correction (bc) used to convert a single-band flux into a bolometric luminosity. we show, using star clusters, that rsgs evolve to later spectral types as they approach sn, which in turn causes the bc to become larger. failure to account for this results in a systematic underestimate of a star's luminosity, and hence its initial mass. using our empirically motivated bcs we reappraise the ii-p and ii-l sne that have their progenitors detected in pre-explosion imaging. fitting an initial mass function to these updated masses results in an increased upper mass cut-off of mhi = 19.0^{+2.5}_{-1.3} m⊙, with a 95 per cent upper confidence limit of <27 m⊙. accounting for finite sample size effects and systematic uncertainties in the mass-luminosity relationship raises the cut-off to mhi = 25 m⊙ (<33 m⊙, 95 per cent confidence). we therefore conclude that there is currently no strong evidence for `missing' high-mass progenitors to core-collapse sne. | the initial masses of the red supergiant progenitors to type ii supernovae |
mounting evidence indicates that neutrinos likely undergo fast flavor conversion (ffc) in at least some core-collapse supernovae. outcomes of ffc, however, remain highly uncertain. here we study the cascade of flavor-field power from large angular scales in momentum space down to small ones, showing that ffc enhances this process and thereby hastens relaxation. cascade also poses a computational challenge, which is present even if the flavor field is stable: when power reaches the smallest angular scale of the calculation, error from truncating the angular-moment expansion propagates back to larger scales, to disastrous effect on the overall evolution. essentially the same issue has prompted extensive work in the context of plasma kinetics. this link suggests new approaches to averting spurious evolution, a problem that presently puts severe limitations on the feasibility of realistic oscillation calculations. | fast oscillations, collisionless relaxation, and spurious evolution of supernova neutrino flavor |
the cosmic distance ladder is the succession of techniques by which it is possible to determine distances to astronomical objects. here, we present a new method to build the cosmic distance ladder, going from local astrophysical measurements to the cmb. instead of relying on high-redshift cosmography in order to model the luminosity-distance relation and calibrate supernovae with bao, we exploit directly the distance-duality relation dl = (1 + z)2da - valid if photon number is conserved and gravity is described by a metric theory. the advantage is that the results will not depend on the parametrization of the luminosity-distance relation at z > 0.15: no model is adopted in order to calibrate bao with supernovae. this method yields local measurements of the hubble constant and deceleration parameter. furthermore, it can directly assess the impact of bao observations on the strong 4-5σ tension between local and global h0. using the latest supernova, bao and cmb observations, we found a consistently low value of q0 and strong inconsistency between angular-only bao constraints and anisotropic bao measurements, which are, or not, in agreement with cmb depending on the kind of analysis (see table 4). we conclude that, in order to understand the reasons behind the h0 crisis, a first step should be clarifying the tension between angular and perpendicular anisotropic bao as this will help understanding if new physics is required at the pre-recombination epoch or/and during the dark energy era. | a new method to build the (inverse) distance ladder |
stars that start their lives with spectral types o and early b are the progenitors of core-collapse supernovae, long gamma-ray bursts, neutron stars, and black holes. these massive stars are the primary sources of stellar feedback in star-forming galaxies. at low metallicities, the properties of massive stars and their evolution are not yet fully explored. here we report a spectroscopic study of 320 massive stars of spectral types o (23 stars) and b (297 stars) in the wing of the small magellanic cloud (smc). the spectra, which we obtained with the eso very large telescope, were analyzed using state-of-the-art stellar atmosphere models, and the stellar parameters were determined. we find that the stellar winds of our sample stars are generally much weaker than theoretically expected. the stellar rotation rates show broad, tentatively bimodal distributions. the upper hertzsprung-russell diagram (hrd) is well populated by the stars of our sample from a specific field in the smc wing. a few very luminous o stars are found close to the main sequence, while all other, slightly evolved stars obey a strict luminosity limit. considering additional massive stars in evolved stages, with published parameters and located all over the smc, essentially confirms this picture. the comparison with single-star evolutionary tracks suggests a dichotomy in the fate of massive stars in the smc. only stars with an initial mass below ∼30 m⊙ seem to evolve from the main sequence to the cool side of the hrd to become a red supergiant and to explode as type ii-p supernova. in contrast, stars with initially more than ∼30 m⊙ appear to stay always hot and might evolve quasi chemically homogeneously, finally collapsing to relatively massive black holes. however, we find no indication that chemical mixing is correlated with rapid rotation. we measured the key parameters of stellar feedback and established the links between the rates of star formation and supernovae. our study demonstrates that in metal-poor environments stellar feedback is dominated by core-collapse supernovae in combination with winds and ionizing radiation supplied by a few of the most massive stars. we found indications of the stochastic mode of massive star formation, where the resulting stellar population is fully capable of producing large-scale structures such as the supergiant shell smc-sgs 1 in the wing. the low level of feedback in metal-poor stellar populations allows star formation episodes to persist over long timescales. tables b.1, b.2, and b.4 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/625/a104based on observations at the european southern observatory very large telescope in program 086.d-0167(a). | testing massive star evolution, star formation history, and feedback at low metallicity. spectroscopic analysis of ob stars in the smc wing |
we constrain tilted spatially-flat and untilted nonflat xcdm dynamical dark energy inflation parameterizations using planck 2015 cosmic microwave background (cmb) anisotropy data and recent baryonic acoustic oscillations distance measurements, type ia supernovae data, hubble parameter observations, and growth rate measurements. inclusion of the four non-cmb data sets results in a significant strengthening of the evidence for nonflatness in the nonflat xcdm model from 1.1σ for the cmb data alone to 3.4σ for the full data combination. in this untilted nonflat xcdm case the data favor a spatially-closed model in which spatial curvature contributes a little less than a percent of the current cosmological energy budget; they also mildly favor dynamical dark energy over a cosmological constant at 1.2σ . these data are also better fit by the flat-xcdm parameterization than by the standard λ cdm model, but only at 0.3σ significance. current data is unable to rule out dark energy dynamics. the nonflat xcdm parameterization is compatible with the dark energy survey limits on the present value of the rms mass fluctuations amplitude (σ 8) as a function of the present value of the nonrelativistic matter density parameter (ωm). however, it does not provide as good a fit to the higher multipole cmb temperature anisotropy data as does the standard tilted flat-λcdm model. a number of measured cosmological parameter values differ significantly when determined using the tilted flat-xcdm and the nonflat xcdm parameterizations, including the baryonic matter density parameter and the reionization optical depth. | observational constraints on the tilted flat-xcdm and the untilted nonflat xcdm dynamical dark energy inflation parameterizations |
our statistical understanding of galaxy evolution is fundamentally driven by objects that lie above the surface-brightness limits of current wide-area surveys (μ ∼ 23 mag arcsec-2). while both theory and small, deep surveys have hinted at a rich population of low-surface-brightness galaxies (lsbgs) fainter than these limits, their formation remains poorly understood. we use horizon-agn, a cosmological hydrodynamical simulation to study how lsbgs, and in particular the population of ultra-diffuse galaxies (udgs; μ > 24.5 mag arcsec-2), form and evolve over time. for m_*> 108 m_{⊙}, lsbgs contribute 47, 7, and 6 per cent of the local number, mass, and luminosity densities, respectively (∼85/11/10 per cent for m_*> 107 m_{⊙}). today's lsbgs have similar dark-matter fractions and angular momenta to high-surface-brightness galaxies (hsbgs; μ < 23 mag arcsec-2), but larger effective radii (×2.5 for udgs) and lower fractions of dense, star-forming gas (more than ×6 less in udgs than hsbgs). lsbgs originate from the same progenitors as hsbgs at z > 2. however, lsbg progenitors form stars more rapidly at early epochs. the higher resultant rate of supernova-energy injection flattens their gas-density profiles, which, in turn, creates shallower stellar profiles that are more susceptible to tidal processes. after z ∼ 1, tidal perturbations broaden lsbg stellar distributions and heat their cold gas, creating the diffuse, largely gas-poor lsbgs seen today. in clusters, ram-pressure stripping provides an additional mechanism that assists in gas removal in lsbg progenitors. our results offer insights into the formation of a galaxy population that is central to a complete understanding of galaxy evolution, and that will be a key topic of research using new and forthcoming deep-wide surveys. | the formation and evolution of low-surface-brightness galaxies |
radio emission is a key indicator of star formation activity in galaxies, but the radio luminosity-star formation relation has to date been studied almost exclusively at frequencies of 1.4 ghz or above. at lower radio frequencies, the effects of thermal radio emission are greatly reduced, and so we would expect the radio emission observed to be completely dominated by synchrotron radiation from supernova-generated cosmic rays. as part of the lofar surveys key science project, the herschel-atlas ngp field has been surveyed with lofar at an effective frequency of 150 mhz. we select a sample from the mpa-jhu catalogue of sloan digital sky survey galaxies in this area: the combination of herschel, optical and mid-infrared data enable us to derive star formation rates (sfrs) for our sources using spectral energy distribution fitting, allowing a detailed study of the low-frequency radio luminosity-star formation relation in the nearby universe. for those objects selected as star-forming galaxies (sfgs) using optical emission line diagnostics, we find a tight relationship between the 150 mhz radio luminosity (l150) and sfr. interestingly, we find that a single power-law relationship between l150 and sfr is not a good description of all sfgs: a broken power-law model provides a better fit. this may indicate an additional mechanism for the generation of radio-emitting cosmic rays. also, at given sfr, the radio luminosity depends on the stellar mass of the galaxy. objects that were not classified as sfgs have higher 150-mhz radio luminosity than would be expected given their sfr, implying an important role for low-level active galactic nucleus activity. | lofar/h-atlas: the low-frequency radio luminosity-star formation rate relation |
we present new herschel photometric and spectroscopic observations of supernova 1987a, carried out in 2012. our dedicated photometric measurements provide new 70 μm data and improved imaging quality at 100 and 160 μm compared to previous observations in 2010. our herschel spectra show only weak co line emission, and provide an upper limit for the 63 μm [o i] line flux, eliminating the possibility that line contaminations distort the previously estimated dust mass. the far-infrared spectral energy distribution (sed) is well fitted by thermal emission from cold dust. the newly measured 70 μm flux constrains the dust temperature, limiting it to nearly a single temperature. the far-infrared emission can be fitted by 0.5 ± 0.1 m ⊙ of amorphous carbon, about a factor of two larger than the current nucleosynthetic mass prediction for carbon. the observation of sio molecules at early and late phases suggests that silicates may also have formed and we could fit the sed with a combination of 0.3 m ⊙ of amorphous carbon and 0.5 m ⊙ of silicates, totalling 0.8 m ⊙ of dust. our analysis thus supports the presence of a large dust reservoir in the ejecta of sn 1987a. the inferred dust mass suggests that supernovae can be an important source of dust in the interstellar medium, from local to high-redshift galaxies. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa. pacs has been developed by a consortium of institutes led by mpe (germany) and including uvie (austria); ku leuven, csl, imec (belgium); cea, lam (france); mpia (germany); inaf-ifsi/oaa/oap/oat, lens, sissa (italy); iac (spain). this development has been supported by the funding agencies bmvit (austria), esa-prodex (belgium), cea/cnes (france), dlr (germany), asi/inaf (italy), and cicyt/mcyt (spain). spire has been developed by a consortium of institutes led by cardiff university (uk) and including univ. lethbridge (canada); naoc (china); cea, lam (france); ifsi, univ. padua (italy); iac (spain); stockholm observatory (sweden); imperial college london, ral, ucl-mssl, ukatc, univ. sussex (uk); and caltech, jpl, nhsc, univ. colorado (usa). this development has been supported by national funding agencies: csa (canada); naoc (china); cea, cnes, cnrs (france); asi (italy); mcinn (spain); snsb (sweden); stfc and uksa (uk); and nasa (usa). | a stubbornly large mass of cold dust in the ejecta of supernova 1987a |
the potential energy from a time-dependent scalar field provides a possible explanation for the observed cosmic acceleration. in this paper, we investigate how the redshift vs brightness data from the recent pantheon+ survey of type ia supernovae constrain the possible evolution of a single scalar field for the period of time (roughly half the age of the universe) over which supernova data are available. taking a linear approximation to the potential, we find that models providing a good fit to the data typically have a decreasing potential energy at present (accounting for over 99% of the allowed parameter space) with a significant variation in scalar potential ($\langle {\rm range}(v)/v_0 \rangle \approx 0.97$) over the period of time corresponding to the available data ($z < 2.3$). including quadratic terms in the potential, the data can be fit well for a wide range of possible potentials including those with positive or negative $v_2$ of large magnitude, and models where the universe has already stopped accelerating. we describe a few degeneracies and approximate degeneracies in the model that help explain the somewhat surprising range of allowed potentials. | possible hints of decreasing dark energy from supernova data |
advanced ligo and virgo detected 10 binary black holes (bbhs) in their first two observing runs (o1 and o2). analysis of these events found evidence for a dearth of bbhs with component masses greater than ∼45 m⊙, as would be expected from pair-instability supernovae. meanwhile, a standalone analysis of the merger gw170729 found its primary mass to be {m}1={51.2}-11.0+16.2 {m}⊙, which appears to be in contradiction with the existence of a limit at ∼45 m⊙. in this work, we argue that the masses of individual events can only be evaluated with reference to the full population. when gw170729 is analyzed jointly with the remaining detections, its inferred primary mass tightens considerably, to {m}1={38.9}-4.5+7.3 {m}⊙ . in the presence of noise, apparent outliers in the detected distribution are inevitable. we discuss methods of distinguishing between statistical fluctuations and true population outliers using posterior predictive tests. applying these tests to o1 and o2, we find that the 10 detections are consistent with even the simplest power-law plus maximum-mass model considered by the ligo-virgo collaboration, supporting the claim that gw170729 is not a population outlier. we also provide non-parametric constraints on the rate of high-mass mergers and conservatively bound the rate of mergers with m1 > 45 m⊙ at {2.8}-2.0+5.4% of the total merger rate. after 100 detections like those of o1 and o2 from a population with a maximum primary mass of 45 m⊙, it would be common for the most massive system to have an observed maximum-likelihood mass m1 ≳ 70 m⊙. | the most massive binary black hole detections and the identification of population outliers |
despite being a well understood phenomenon in the context of current terrestrial experiments, neutrino flavor conversions in dense astrophysical environments probably represent one of the most challenging open problems in neutrino physics. apart from being theoretically interesting, such a problem has several phenomenological implications in cosmology and in astrophysics, including the primordial nucleosynthesis of light elements abundance and other cosmological observables, nucleosynthesis of heavy nuclei, and the explosion of massive stars. in this review, we briefly summarize the state of the art on this topic, focusing on three environments: early universe, core-collapse supernovae, and compact binary mergers. | neutrino flavor conversions in high-density astrophysical and cosmological environments |
in astrophysical scenarios with large neutrino density, like supernovae and the early universe, the presence of neutrino-neutrino interactions can give rise to collective flavor oscillations in the out-of-equilibrium collective dynamics of a neutrino cloud. the role of quantum correlations in these phenomena is not yet well understood, in large part due to complications in solving for the real-time evolution of the strongly coupled many-body system. future fault-tolerant quantum computers hold the promise to overcome much of these limitations and provide direct access to the correlated neutrino dynamic. in this work, we present the first simulation of a small system of interacting neutrinos using current generation quantum devices. we introduce a strategy to overcome limitations in the natural connectivity of the qubits and use it to track the evolution of entanglement in real-time. the results show the critical importance of error-mitigation techniques to extract meaningful results for entanglement measures using noisy, near term, quantum devices. | simulation of collective neutrino oscillations on a quantum computer |
some studies of stars' multielement abundance distributions suggest at least 5-7 significant dimensions, but others show that many elemental abundances can be predicted to high accuracy from [fe/h] and [mg/fe] (or [fe/h] and age) alone. we show that both propositions can be, and are, simultaneously true. we adopt a machine-learning technique known as normalizing flow to reconstruct the probability distribution of milky way disk stars in the space of 15 elemental abundances measured by apogee. conditioning on t eff and $\mathrm{log}\,g$ minimizes the differential systematics. after further conditioning on [fe/h] and [mg/fe], the residual scatter for most abundances is σ [x/h] ≲ 0.02 dex, consistent with apogee's reported statistical uncertainties of ~0.01-0.015 dex and intrinsic scatter of 0.01-0.02 dex. despite the small scatter, residual abundances display clear correlations between elements, which we show are too large to be explained by measurement uncertainties or by the finite sampling noise. we must condition on at least seven elements to reduce the correlations to a level consistent with the observational uncertainties. our results demonstrate that cross-element correlations are a much more sensitive probe of a hidden structure than dispersion, and they can be measured precisely in a large sample even if the star-by-star measurement noise is comparable to the intrinsic scatter. we conclude that many elements have an independent story to tell, even for the mundane disk stars and elements produced by the core-collapse and type ia supernovae. the only way to learn these lessons is to measure the abundances directly, and not merely infer them. | how many elements matter? |
charged-current neutrino processes such as νe+n ⇌p +e- and ν¯ e+p ⇌n +e+ destroy the flavor coherence among the weak-interaction states of a single neutrino and thus damp its flavor oscillation. in a dense neutrino gas such as that inside a core-collapse supernova or the black hole accretion disk formed in a compact binary merger, however, these "collision" processes can trigger large flavor conversion in cooperation with the strong neutrino-neutrino refraction. we show that there exist two types of collisional flavor instability in a homogeneous and isotropic neutrino gas which are identified by the dependence of their real frequencies on the neutrino density nν. the instability transitions from one type to the other and exhibits a resonancelike behavior in the region where the net electron lepton number of the neutrino gas is negligible. in the transition region, the flavor instability grows exponentially at a rate ∝nν1 /2. we find that the neutrino gas in the black hole accretion disk is susceptible to the collision-induced flavor conversion where the neutrino densities are the highest. further investigations are needed to confirm if the collisional flavor instability will indeed result in the production of large amounts of heavy-lepton flavor neutrinos in this environment which would have important ramifications in its subsequent evolution. | collisional flavor instability in dense neutrino gases |
we describe the operation and performance of the difference imaging pipeline (diffimg) used to detect transients in deep images from the dark energy survey supernova program (des-sn) in its first observing season from 2013 august through 2014 february. des-sn is a search for transients in which ten 3 deg2 fields are repeatedly observed in the g, r, i, z passbands with a cadence of about 1 week. the observing strategy has been optimized to measure high-quality light curves and redshifts for thousands of type ia supernovae (sne ia) with the goal of measuring dark energy parameters. the essential diffimg functions are to align each search image to a deep reference image, do a pixel-by-pixel subtraction, and then examine the subtracted image for significant positive detections of point-source objects. the vast majority of detections are subtraction artifacts, but after selection requirements and image filtering with an automated scanning program, there are ∼130 detections per deg2 per observation in each band, of which only ∼25% are artifacts. of the ∼7500 transients discovered by des-sn in its first observing season, each requiring a detection on at least two separate nights, monte carlo (mc) simulations predict that 27% are expected to be sne ia or core-collapse sne. another ∼30% of the transients are artifacts in which a small number of observations satisfy the selection criteria for a single-epoch detection. spectroscopic analysis shows that most of the remaining transients are agns and variable stars. fake sne ia are overlaid onto the images to rigorously evaluate detection efficiencies and to understand the diffimg performance. the diffimg efficiency measured with fake sne agrees well with expectations from a mc simulation that uses analytical calculations of the fluxes and their uncertainties. in our 8 “shallow” fields with single-epoch 50% completeness depth ∼23.5, the sn ia efficiency falls to 1/2 at redshift z ≈ 0.7; in our 2 “deep” fields with mag-depth ∼24.5, the efficiency falls to 1/2 at z ≈ 1.1. a remaining performance issue is that the measured fluxes have additional scatter (beyond poisson fluctuations) that increases with the host galaxy surface brightness at the transient location. this bright-galaxy issue has minimal impact on the sne ia program, but it may lower the efficiency for finding fainter transients on bright galaxies. | the difference imaging pipeline for the transient search in the dark energy survey |
swope supernova survey 2017a (sss17a) was discovered as the first optical counterpart to the gravitational wave event gw170817. although its light curve on the timescale of weeks roughly matches the expected luminosity and red color of an r-process powered transient, the explanation for the blue emission from high velocity material over the first few days is not as clear. here we show that the power-law evolution of the luminosity, temperature, and photospheric radius during these early times can be explained by cooling of shock-heated material around the neutron star merger. this heating is likely from the interaction of the gamma-ray burst jet with merger debris, the so-called cocoon emission. we summarize the properties of this emission and provide formulae that can be used to study future detections of shock cooling from merging neutron stars. this argues that optical transient surveys should search for such early, blue light if they wish to find off-axis gamma-ray bursts and double neutron star gravitational wave events as soon as possible after the merger. | evidence for cocoon emission from the early light curve of sss17a |
present and upcoming time-domain astronomy efforts, in part driven by gravitational-wave follow-up campaigns, will unveil a variety of rare explosive transients in the sky. here, we focus on pulsational pair-instability evolution, which can result in signatures that are observable with electromagnetic and gravitational waves. we simulated grids of bare helium stars to characterize the resulting black hole (bh) masses together with the ejecta composition, velocity, and thermal state. we find that the stars do not react "elastically" to the thermonuclear ignition in the core: there is not a one-to-one correspondence between pair-instability driven ignition and mass ejections, which causes ambiguity as to what is an observable pulse. in agreement with previous studies, we find that for initial helium core masses of 37.5 m⊙ ≲ mhe, init ≲ 41 m⊙, corresponding to carbon-oxygen core masses 27.5 m⊙ ≲ mco ≲ 30.1 m⊙, the explosions are not strong enough to affect the surface. with increasing initial helium core mass, they become progressively stronger causing first large radial expansion (41 m⊙ ≲ mhe, init ≲ 42 m⊙, corresponding to 30.1 m⊙ ≲ mco ≲ 30.8 m⊙) and, finally, also mass ejection episodes (for mhe, init ≳ 42 m⊙, or mco ≳ 30.8 m⊙). the lowest mass helium core to be fully disrupted in a pair-instability supernova is mhe, init ≃ 80 m⊙, corresponding to mco ≃ 55 m⊙. models with mhe, init ≳ 200 m⊙ (mco ≳ 114 m⊙) reach the photodisintegration regime, resulting in bhs with masses of mbh ≳ 125 m⊙. although this is currently considered unlikely, if bhs from these models form via (weak) explosions, the previously-ejected material might be hit by the blast wave and convert kinetic energy into observable electromagnetic radiation. we characterize the hydrogen-free circumstellar material from the pulsational pair-instability of helium cores by simply assuming that the ejecta maintain a constant velocity after ejection. we find that our models produce helium-rich ejecta with mass of 10-3 m⊙ ≲ mcsm ≲ 40 m⊙, the larger values corresponding to the more massive progenitor stars. these ejecta are typically launched at a few thousand km s-1 and reach distances of ∼1012 - 1015 cm before the core-collapse of the star. the delays between mass ejection events and the final collapse span a wide and mass-dependent range (from subhour to 104 years), and the shells ejected can also collide with each other, powering supernova impostor events before the final core-collapse. the range of properties we find suggests a possible connection with (some) type ibn supernovae. | predictions for the hydrogen-free ejecta of pulsational pair-instability supernovae |
an important part of cosmological model fitting relies on correlating distance indicators of objects (for example, type ia supernovae) with their redshift, often illustrated on a hubble diagram. comparing the observed correlation with a homogeneous model is one of the key pieces of evidence for dark energy. the presence of cosmic structures introduces a bias and scatter, mainly due to gravitational lensing and peculiar velocities but also due to smaller nonlinear relativistic contributions that are more difficult to account for. for the first time we perform ray tracing onto halos in a relativistic n-body simulation. our simulation is the largest that takes into account all leading-order corrections from general relativity in the evolution of structure, and we present a novel methodology for working out the nonlinear projection of that structure onto the observer's past light cone. we show that the mean of the bias in the hubble diagram is indeed as small as expected from perturbation theory. however, the distribution of sources is significantly skewed with a very long tail of highly magnified objects, and we illustrate that the bias of cosmological parameters strongly depends on the function of distance which we consider. | bias and scatter in the hubble diagram from cosmological large-scale structure |
we perform general relativistic one-dimensional supernova (sn) simulations to identify observable signatures of enhanced axion emission from the pion-induced reaction π-+p →n +a inside a newly born protoneutron star (pns). we focus on the early evolution after the onset of the supernova explosion to predict the temporal and spectral features of the neutrino and axion emission during the first 10 s. pions are included as explicit new degrees of freedom in hot and dense matter. their thermal population and their role in axion production are both determined consistently to include effects due to their interactions with nucleons. for a wide range of ambient conditions encountered inside a pns, we find that the pion-induced axion production dominates over nucleon-nucleon bremsstrahlung processes. by consistently including the role of pions on the dense matter equation of state and on the energy loss, our simulations predict robust discernible features of neutrino and axion emission from a galactic supernova that can be observed in terrestrial detectors. for axion couplings that are compatible with current bounds, we find a significant suppression with time of the neutrino luminosity during the first 10 s. this suggests that current bounds derived from the neutrino signal from sn 1987a can be improved and that future galactic supernovae may provide significantly more stringent constraints. | observable signatures of enhanced axion emission from protoneutron stars |
type ia supernovae (sne ia) span a range of luminosities and timescales, from rapidly evolving subluminous to slowly evolving overluminous subtypes. previous theoretical work has, for the most part, been unable to match the entire breadth of observed sne ia with one progenitor scenario. here, for the first time, we apply non-local thermodynamic equilibrium radiative transfer calculations to a range of accurate explosion models of sub-chandrasekhar-mass white dwarf detonations. the resulting photometry and spectra are in excellent agreement with the range of observed nonpeculiar sne ia through 15 days after the time of b-band maximum, yielding one of the first examples of a quantitative match to the entire phillips relation. the intermediate-mass element velocities inferred from theoretical spectra at maximum light for the more massive white dwarf explosions are higher than those of bright observed sne ia, but these and other discrepancies likely stem from the one-dimensional nature of our explosion models and will be improved upon by future non-local thermodynamic equilibrium radiation transport calculations of multidimensional sub-chandrasekhar-mass white dwarf detonations. | non-local thermodynamic equilibrium radiative transfer simulations of sub-chandrasekhar-mass white dwarf detonations |
analyses of type ia supernovae (sne ia) have found puzzling correlations between their standardized luminosities and host galaxy properties: sne ia in high-mass, passive hosts appear brighter than those in lower mass, star-forming hosts. we examine the host galaxies of sne ia in the dark energy survey 3-yr spectroscopically confirmed cosmological sample, obtaining photometry in a series of 'local' apertures centred on the sn, and for the global host galaxy. we study the differences in these host galaxy properties, such as stellar mass and rest-frame u - r colours, and their correlations with sn ia parameters including hubble residuals. we find all hubble residual steps to be >3σ in significance, both for splitting at the traditional environmental property sample median and for the step of maximum significance. for stellar mass, we find a maximal local step of 0.098 ± 0.018 mag; ∼0.03 mag greater than the largest global stellar mass step in our sample (0.070 ± 0.017 mag). when splitting at the sample median, differences between local and global u - r steps are small, both ∼0.08 mag, but are more significant than the global stellar mass step (0.057 ± 0.017 mag). we split the data into sub-samples based on sn ia light-curve parameters: stretch (x1) and colour (c), finding that redder objects (c > 0) have larger hubble residual steps, for both stellar mass and u - r, for both local and global measurements, of ∼0.14 mag. additionally, the bluer (star-forming) local environments host a more homogeneous sn ia sample, with local u - r rms scatter as low as 0.084 ± 0.017 mag for blue (c < 0) sne ia in locally blue u - r environments. | the effect of environment on type ia supernovae in the dark energy survey three-year cosmological sample |
we compare the elemental abundance patterns of ∼200 extremely metal-poor (emp; [fe/h] < -3) stars to the supernova yields of metal-free stars, in order to obtain insights into the characteristic masses of the first (population iii or pop iii) stars in the universe. the supernova yields are prepared with nucleosynthesis calculations of metal-free stars with various initial masses (m = 13, 15, 25, 40 and 100 m ⊙) and explosion energies (e 51 = e/1051[erg] = 0.5-60), to include low-energy, normal-energy, and high-energy explosions. we adopt the mixing-fallback model, to take into account possible asymmetry in the supernova explosions, and the yields that best fit the observed abundance patterns of the emp stars are searched by varying the model parameters. we find that the abundance patterns of the emp stars are predominantly best-fitted by the supernova yields with initial masses m < 40 m ⊙, and that more than than half of the stars are best-fitted by the m = 25 m ⊙ hypernova (e 51 = 10) models. the results also indicate that the majority of the primordial supernovae have ejected 10-2-10-1 m ⊙ of 56ni, leaving behind a compact remnant (either a neutron star or a black hole), with a mass in the range of ∼1.5-5 m ⊙. these results suggest that the masses of the first stars responsible for the first metal enrichment are predominantly <40 m ⊙. this implies that the higher-mass first stars were either less abundant, directly collapsed into a black hole without ejecting heavy elements, or a supernova explosion of a higher-mass first star inhibits the formation of the next generation of low-mass stars at [fe/h] < -3. | the initial mass function of the first stars inferred from extremely metal-poor stars |
fast and collisional flavor instabilities possibly occur in the neutrino decoupling regions of core-collapse supernovae and neutron-star mergers. to gain a better understanding of the relevant flavor dynamics, we numerically solve for the collisionally unstable evolution in a homogeneous, anisotropic model. in these calculations collisional instability is precipitated by unequal neutrino and antineutrino scattering rates. we compare the solutions obtained using neutral-current and charged-current interactions. we then study the nonlinear development of fast instabilities subjected to asymmetric scattering rates, finding evidence that the onset of collisional instability is hastened by fast oscillations. we also discuss connections to other recent works on collision-affected fast flavor conversion. | collisional instabilities of neutrinos and their interplay with fast flavor conversion in compact objects |
we study the formation of galactic outflows from supernova (sn) explosions with the moving-mesh code arepo in a stratified column of gas with a surface density similar to the milky way disk at the solar circle. we compare different simulation models for sn placement and energy feedback, including cosmic rays (crs), and find that models that place sne in dense gas and account for cr diffusion are able to drive outflows with similar mass loading as obtained from a random placement of sne with no crs. despite this similarity, cr-driven outflows differ in several other key properties including their overall clumpiness and velocity. moreover, the forces driving these outflows originate in different sources of pressure, with the cr diffusion model relying on non-thermal pressure gradients to create an outflow driven by internal pressure and the random-placement model depending on kinetic pressure gradients to propel a ballistic outflow. crs therefore appear to be non-negligible physics in the formation of outflows from the interstellar medium. | the role of cosmic-ray pressure in accelerating galactic outflows |
the lattice dynamics and high-temperature structural transition in sns and snse are investigated via inelastic neutron scattering, high-resolution raman spectroscopy and anharmonic first-principles simulations. we uncover a spectacular, extreme softening and reconstruction of an entire manifold of low-energy acoustic and optic branches across a structural transition, reflecting strong directionality in bonding strength and anharmonicity. further, our results solve a prior controversy by revealing the soft-mode mechanism of the phase transition that impacts thermal transport and thermoelectric efficiency. our simulations of anharmonic phonon renormalization go beyond low-order perturbation theory and capture these striking effects, showing that the large phonon shifts directly affect the thermal conductivity by altering both the phonon scattering phase space and the group velocities. these results provide a detailed microscopic understanding of phase stability and thermal transport in technologically important materials, providing further insights on ways to control phonon propagation in thermoelectrics, photovoltaics, and other materials requiring thermal management. | extended anharmonic collapse of phonon dispersions in sns and snse |
in this review, we first reassess the supernova remnant paradigm for the origin of galactic cosmic rays in the light of recent cosmic-ray data acquired by the voyager 1 spacecraft. we then describe the theory of light-element nucleosynthesis by nuclear interaction of cosmic rays with the interstellar medium and outline the problem of explaining the measured beryllium abundances in old halo stars of low metallicity with the standard model of the galactic cosmic-ray origin. we then discuss the various cosmic-ray models proposed in the literature to account for the measured evolution of the light elements in the milky way, and point out the difficulties that they all encounter. it seems to us that, among all possibilities, the superbubble model provides the most satisfactory explanation for these observations. | particle acceleration by supernova shocks and spallogenic nucleosynthesis of light elements |
we report on the gravitational-wave signal computed in the context of a three-dimensional simulation of a core-collapse supernova explosion of a 15 m⊙ star. the simulation was performed with our neutrino hydrodynamics code chimera. we detail the gravitational wave strains as a function of time, for both polarizations, and discuss their physical origins. we also present the corresponding spectral signatures. gravitational wave emission in our model has two key features: low-frequency emission (less than 200 hz) emanates from the gain layer as a result of neutrino-driven convection and the standing accretion shock instability (sasi), and high-frequency emission (greater than 600 hz) emanates from the proto-neutron star due to ledoux convection within it. the high-frequency emission dominates the gravitational wave emission in our model and emanates largely from the convective layer itself, not from the convectively stable layer above it, due to convective overshoot. moreover, the low-frequency emission emanates from the gain layer itself, not from the proto-neutron star, due to accretion onto it. we provide evidence of the sasi in our model and demonstrate that the peak of our low-frequency gravitational wave emission spectrum corresponds to it. given its origin in the gain layer, we classify the sasi emission in our model as p-mode emission and assign a purely acoustic origin, not a vortical-acoustic origin, to it. we compare the results of our three-dimensional model analysis with those obtained from the model's two-dimensional counterpart and find a significant reduction in the strain amplitudes in the former case, as well as significant reductions in all related quantities. our dominant proto-neutron star gravitational wave emission is not well characterized by emission from surface g modes, complicating the relationship between peak frequencies observed and the mass and radius of the proto-neutron star expressed by analytic estimates under the assumption of surface g-mode emission. we present our frequency normalized characteristic strain along with the sensitivity curves of current- and next-generation gravitational wave detectors. this simple analysis indicates that the spectrum of gravitational wave emission between approximately 20 hz and approximately 1 khz, stemming from neutrino-driven convection, the sasi, accretion onto the proto-neutron star, and proto-neutron star convection, will be accessible for a galactic event. | gravitational-wave signal of a core-collapse supernova explosion of a 15 m⊙ star |
we report the discovery of a nearby dwarf galaxy in the constellation of hydrus, between the large (lmc) and the small magellanic clouds (smc). hydrus 1 is a mildly elliptical ultrafaint system with luminosity mv ∼ -4.7 and size 53 ± 3 pc, located 28 kpc from the sun and 24 kpc from the lmc. from spectroscopy of ∼30 member stars, we measure a velocity dispersion of 2.7 ± 0.5 km s-1 and find tentative evidence for a radial velocity gradient consistent with 3 km s-1 rotation. hydrus 1's velocity dispersion indicates that the system is dark matter dominated, but its dynamical mass-to-light ratio m/l=66^{+29}_{-20} is significantly smaller than typical for ultrafaint dwarfs at similar luminosity. the kinematics and spatial position of hydrus 1 make it a very plausible member of the family of satellites brought into the milky way by the magellanic clouds. while hydrus 1's proximity and well-measured kinematics make it a promising target for dark matter annihilation searches, we find no evidence for significant gamma-ray emission from hydrus 1. the new dwarf is a metal-poor galaxy with a mean metallicity [fe/h]=-2.5 and [fe/h] standard deviation of 0.4 dex, similar to other systems of similar luminosity. α abundances of hyi 1 members indicate that star formation was extended, lasting between 0.1 and 1 gyr, with self-enrichment dominated by supernova ia. the dwarf also hosts a highly carbon-enhanced extremely metal-poor star with [fe/h]∼-3.2 and [c/fe] ∼ +3.0. | snake in the clouds: a new nearby dwarf galaxy in the magellanic bridge* |
we present new large binocular telescope, hubble space telescope, and spitzer space telescope data for the failed supernova candidate n6946-bh1. we also report an unsuccessful attempt to detect the candidate with chandra. the ~300 000 $\, \mathrm{l}_\odot$ red supergiant progenitor underwent an outburst in 2009 and has since disappeared in the optical. in the lbt data from 2008 may through 2019 october, the upper limit on any increase in the r-band luminosity of the source is $2000 \, \mathrm{l}_\odot$. hst and spitzer observations show that the source continued to fade in the near-ir and mid-ir, fading by approximately a factor of 2 between 2015 october and 2017 september to 2900 $\, \mathrm{l}_\odot$ at hband (f160w). models of the spectral energy distribution are inconsistent with a surviving star obscured either by an ongoing wind or dust formed in the transient. the disappearance of n6946-bh1 remains consistent with a failed supernova, but the post-failure phenomenology requires further theoretical study. | the search for failed supernovae with the large binocular telescope: n6946-bh1, still no star |
a dense neutrino medium can experience collective flavor oscillations through nonlinear neutrino-neutrino refraction. to make this multi-dimensional flavor transport problem more tractable, all existing studies have assumed certain symmetries (e.g., the spatial homogeneity and directional isotropy in the early universe) to reduce the dimensionality of the problem. in this work we show that, if both the directional and spatial symmetries are not enforced in the neutrino line model, collective oscillations can develop in the physical regimes where the symmetry-preserving oscillation modes are stable. our results suggest that collective neutrino oscillations in real astrophysical environments (such as core-collapse supernovae and black-hole accretion discs) can be qualitatively different from the predictions based on existing models in which spatial and directional symmetries are artificially imposed. | flavor instabilities in the neutrino line model |
we have performed r -process calculations for matter ejected dynamically in neutron star mergers based on a complete set of trajectories from a three-dimensional relativistic smoothed particle hydrodynamic simulation with a total ejected mass of ∼1.7 ×10-3m⊙ . our calculations consider an extended nuclear network, including spontaneous, β - and neutron-induced fission and adopting fission yield distributions from the abla code. in particular we have studied the sensitivity of the r -process abundances to nuclear masses by using different models. most of the trajectories, corresponding to 90% of the ejected mass, follow a relatively slow expansion allowing for all neutrons to be captured. the resulting abundances are very similar to each other and reproduce the general features of the observed r -process abundance (the second and third peaks, the rare-earth peak, and the lead peak) for all mass models as they are mainly determined by the fission yields. we find distinct differences in the predictions of the mass models at and just above the third peak, which can be traced back to different predictions of neutron separation energies for r -process nuclei around neutron number n =130 . in all simulations, we find that the second peak around a ∼130 is produced by the fission yields of the material that piles up in nuclei with a ≳250 due to the substantially longer β -decay half-lives found in this region. the third peak around a ∼195 is generated in a competition between neutron captures and β decays during r -process freeze-out. the remaining trajectories, which contribute 10% by mass to the total integrated abundances, follow such a fast expansion that the r process does not use all the neutrons. this also leads to a larger variation of abundances among trajectories, as fission does not dominate the r -process dynamics. the resulting abundances are in between those associated to the r and s processes. the total integrated abundances are dominated by contributions from the slow abundances and hence reproduce the general features of the observed r -process abundances. we find that, at timescales of weeks relevant for kilonova light curve calculations, the abundance of actinides is larger than the one of lanthanides. this means that actinides can be even more important than lanthanides to determine the photon opacities under kilonova conditions. moreover, we confirm that the amount of unused neutrons may be large enough to give rise to another observational signature powered by their decay. | nuclear robustness of the r process in neutron-star mergers |
recently, barrow holographic dark energy (bhde), based on barrow entropy, has been proposed to describe the late acceleration of the universe. contrary to the earlier analysis of this model in the literature, we consider the bhde with the granda-oliveros length as ir cut-off, as a dynamical vacuum, having a constant equation of state ωλ = −1. we have analytically solved for the hubble parameter and studied the evolution of cosmological parameters. the model is compared with the observational data on hubble parameter (ohd36) and supernovae type ia (sn ia), the pantheon data. in the absence of interaction between the dark sectors, we found that the model predicts a λcdm-like evolution of the universe with an effective cosmological constant. in this case, the model is found to satisfy the generalized second law (gsl), irrespective of the value of the barrow index. the interaction also shows the safe validity of gsl, for the extracted value of the barrow index, δ = 0.063 ± 0.029. the thermodynamic analysis of the model predicts an end de sitter phase of maximum entropy. we performed a dynamical system analysis, which reveals that the end de sitter phase is stable. furthermore, we performed the information criterion analysis using akaike and bayesian information criterion to compare the statistical compatibility of the present model with the standard λcdm model. | barrow holographic dark energy model with go cut-off - an alternative perspective |
we investigate observable signatures of a first-order quantum chromodynamics (qcd) phase transition in the context of core-collapse supernovae. to this end, we conduct axially symmetric numerical relativity simulations with multi-energy neutrino transport, using a hadron-quark hybrid equation of state (eos). we consider four nonrotating progenitor models, whose masses range from 9.6 to 70 m ⊙. we find that the two less-massive progenitor stars (9.6 and 11.2 m ⊙) show a successful explosion, which is driven by the neutrino heating. they do not undergo the qcd phase transition and leave behind a neutron star. as for the more massive progenitor stars (50 and 70 m ⊙), the proto-neutron star (pns) core enters the phase transition region and experiences the second collapse. because of a sudden stiffening of the eos entering to the pure quark matter regime, a strong shock wave is formed and blows off the pns envelope in the 50 m ⊙ model. consequently the remnant becomes a quark core surrounded by hadronic matter, leading to the formation of the hybrid star. however, for the 70 m ⊙ model, the shock wave cannot overcome the continuous mass accretion and it readily becomes a black hole. we find that the neutrino and gravitational wave (gw) signals from supernova explosions driven by the hadron-quark phase transition are detectable for the present generation of neutrino and gw detectors. furthermore, the analysis of the gw detector response reveals unique khz signatures, which will allow us to distinguish this class of supernova explosions from failed and neutrino-driven explosions. | core-collapse supernova simulations and the formation of neutron stars, hybrid stars, and black holes |
diffusive shock acceleration is a prominent mechanism for producing energetic particles in space and in astrophysical systems. such energetic particles have long been predicted to affect the hydrodynamic structure of the shock, in turn leading to cr spectra flatter than the test-particle prediction. however, in this work along with a companion paper, we use self-consistent hybrid (kinetic ion-fluid electron) simulations to show for the first time how cr-modified shocks actually produce steeper spectra. the steepening is driven by the enhanced advection of crs embedded in magnetic turbulence downstream of the shock, in what we call the "postcursor." these results are consistent with multiwavelength observations of supernovae and supernova remnants and have significant phenomenological implications for space/astrophysical shocks in general. | kinetic simulations of cosmic-ray-modified shocks. ii. particle spectra |
we constrain the formation rate of galactic magnetars directly from observations. combining spin-down rates, magnetic activity, and association with supernova remnants, we put a 2σ limit on their galactic formation rate at 2.3-20 kyr^{-1}. this leads to a fraction 0.4_{-0.28}^{+0.6} of neutron stars being born as magnetars. we study evolutionary channels that can account for this rate as well as for the periods, period derivatives, and luminosities of the observed population. we find that their typical magnetic fields at birth are 3 × 1014-1015 g, and that those decay on a timescale of ∼104 yr, implying a maximal magnetar period of pmax ≈ 13 s. a sizable fraction of the magnetars' energy is released in outbursts. giant flares with e ≥ 1046 erg are expected to occur in the galaxy at a rate of ∼ 5 kyr^{-1}. outside our galaxy, such flares remain observable by swift up to a distance of ∼100 mpc, implying a detection rate of ∼ 5 yr^{-1}. the specific form of magnetic energy decay is shown to be strongly tied to the total number of observable magnetars in the galaxy. a systematic survey searching for magnetars could determine the former and inform physical models of magnetic field decay. | formation rates and evolution histories of magnetars |
recent distance ladder determinations of the hubble constant h0 disagree at about the 3.5σ level with the value determined from planck measurements of the cosmic microwave background (cmb) assuming a λcdm† cosmology. this discrepancy has prompted speculation that new physics might be required beyond that assumed in the λcdm model. in this paper, we apply the inverse distance ladder to fit a parametric form of h(z) to baryon acoustic oscillation (bao) and type ia supernova (sne) data together with priors on the sound horizon at the end of the radiation drag epoch, rd. we apply priors on rd, based on inferences from either planck or the wilkinson microwave anisotropy probe (wmap), and demonstrate that these values are consistent with cmb-independent determination of rd derived from measurements of the primordial deuterium abundance, bao and supernova data assuming the λcdm cosmology. the h(z) constraints that we derive are independent of detailed physics within the dark sector at low redshifts, relying only on the validity of the friedmann-robertson-walker (frw) metric of general relativity. for each assumed prior on rd, we find consistency with the inferred value of h0 and the planck λcdm value and corresponding tension with the distance ladder estimate. | model independent h(z) reconstruction using the cosmic inverse distance ladder |
the beyond ultra-deep frontier fields and legacy observations (buffalo) is a 101 orbit + 101 parallel cycle 25 hubble space telescope (hst) treasury program taking data from 2018 to 2020. buffalo will expand existing coverage of the hubble frontier fields (hff) in wide field camera 3/ir f105w, f125w, and f160w and advanced camera for surveys/wfc f606w and f814w around each of the six hff clusters and flanking fields. this additional area has not been observed by hst but is already covered by deep multiwavelength data sets, including spitzer and chandra. as with the original hff program, buffalo is designed to take advantage of gravitational lensing from massive clusters to simultaneously find high-redshift galaxies that would otherwise lie below hst detection limits and model foreground clusters to study the properties of dark matter and galaxy assembly. the expanded area will provide the first opportunity to study both cosmic variance at high redshift and galaxy assembly in the outskirts of the large hff clusters. five additional orbits are reserved for transient follow-up. buffalo data including mosaics, value-added catalogs, and cluster mass distribution models will be released via mast on a regular basis as the observations and analysis are completed for the six individual clusters. | the buffalo hst survey |
the xenon collaboration recently reported an excess of electron recoil events in the low energy region with a significance of around 3.3 σ . an explanation of this excess in terms of thermal dark matter seems challenging. we propose a scenario where dark matter in the milky way halo gets boosted as a result of scattering with the diffuse supernova neutrino background. this interaction can accelerate the dark-matter to semi-relativistic velocities, and this flux, in turn, can scatter with the electrons in the detector, thereby providing a much better fit to the data. we identify regions in the parameter space of dark-matter mass and interaction cross section which satisfy the excess. furthermore, considering the data only hypothesis, we also impose bounds on the dark-matter scattering cross section, which are competitive with bounds from other experiments. | boosted dark matter from diffuse supernova neutrinos |
liu et al. (2019) recently reported the detection of a 68 [+11/-13] solar mass (msun) black hole (bh) paired with an 8.2 [+0.9/-1.2] msun b-type sub-giant star in the 78.9-day spectroscopic binary system lb-1. such a black hole is over twice as massive as any other known stellar-mass black hole with non-compact companions2 and its mass approaches those that result from bh-bh coalescences that are detected by gravitational wave interferometers. its presence in a solar-like metallicity environment challenges conventional theories of massive binary evolution, stellar winds and core-collapse supernovae, so that more exotic scenarios seem to be needed to explain the existence and properties of lb-1. here, we show that the observational diagnostics used to derive the bh mass results from the orbital motion of the b-type star, not that of the bh. as a consequence, no evidence for a massive bh remains in the data, therefore solving the existing tension with formation models of such a massive bh at solar metallicity and with theories of massive star evolution in general. | on the signature of a 70-solar-mass black hole in lb-1 |
context. elements heavier than iron are produced through neutron-capture processes in the different phases of stellar evolution. asymptotic giant branch (agb) stars are believed to be mainly responsible for elements that form through the slow neutron-capture process, while the elements created in the rapid neutron-capture process have production sites that are less understood. knowledge of abundance ratios as functions of metallicity can lead to insight into the origin and evolution of our galaxy and its stellar populations.aims: we aim to trace the chemical evolution of the neutron-capture elements sr, zr, la, ce, nd, sm, and eu in the milky way stellar disk. this will allow us to constrain the formation sites of these elements, as well as to probe the evolution of the galactic thin and thick disks.methods: using spectra of high resolution (42 000 ≲ r ≲ 65 000) and high signal-to-noise (s/n ≳ 200) obtained with the mike and the feros spectrographs, we determine sr, zr, la, ce, nd, sm, and eu abundances for a sample of 593 f and g dwarf stars in the solar neighborhood. the abundance analysis is based on spectral synthesis using one-dimensional, plane-parallel, local thermodynamic equilibrium (lte) model stellar atmospheres calculated with the marcs 2012 code.results: we present abundance results for sr (156 stars), zr (311 stars), la (242 stars), ce (365 stars), nd (395 stars), sm (280 stars), and eu (378 stars). we find that nd, sm, and eu show trends similar to what is observed for the α elements in the [x/fe]-[fe/h] abundance plane. for [sr/fe] and [zr/fe], we find decreasing abundance ratios for increasing metallicity, reaching sub-solar values at super-solar metallicities. [la/fe] and [ce/fe] do not show any clear trend with metallicity, and they are close to solar values at all [fe/h]. the trends of abundance ratios [x/fe] as a function of stellar ages present different slopes before and after 8 gyr.conclusions: the rapid neutron-capture process is active early in the galaxy, mainly in type-ii supernovae from stars in the mass range 8-10 m⊙. europium is almost completely produced by the r-process, but nd and sm show similar trends to eu even if their s-process component is higher. strontium and zr are thought to be mainly produced by the s-process, but show significant enrichment at low metallicity that requires extra r-process production, which probably is different from the classical r-process. finally, la and ce are mainly produced via s-process from agb stars in the mass range 2-4 m⊙, which can be seen by the decrease in [la/eu] and [ce/eu] at [fe/h] ≈ -0.5. the trend of [x/fe] with age could be explained by considering that the decrease in [x/fe] for the thick disk stars can be due to the decrease in type-ii supernovae with time, meaning a reduced enrichment of r-process elements in the interstellar medium. in the thin disk, the trends are flatter, which is probably due to the main production from the s-process being balanced by fe production from type-ia supernovae. this paper includes data gathered with the 6.5 m magellan telescopes at the las campanas observatory, chile and the eso 1.5-m, 2.2-m. and 3.6-m telescopes on la silla, chile (eso proposal id 65.l-0019, 67.b-0108, 76.b-0416, 82.b-0610); and data from uves paranal observatory project (eso ddt program id 266.d-5655).full tables 3 and 4 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/586/a49 | the origin and evolution of r- and s-process elements in the milky way stellar disk |
most type i superluminous supernovae (slsne-i) reported to date have been identified by their high peak luminosities and spectra lacking obvious signs of hydrogen. we demonstrate that these events can be distinguished from normal-luminosity sne (including type ic events) solely from their spectra over a wide range of light-curve phases. we use this distinction to select 19 slsne-i and four possible slsne-i from the palomar transient factory archive (including seven previously published objects). we present 127 new spectra of these objects and combine these with 39 previously published spectra, and we use these to discuss the average spectral properties of slsne-i at different spectral phases. we find that mn ii most probably contributes to the ultraviolet spectral features after maximum light, and we give a detailed study of the o ii features that often characterize the early-time optical spectra of slsne-i. we discuss the velocity distribution of o ii, finding that for some slsne-i this can be confined to a narrow range compared to relatively large systematic velocity shifts. mg ii and fe ii favor higher velocities than o ii and c ii, and we briefly discuss how this may constrain power-source models. we tentatively group objects by how well they match either sn 2011ke or ptf12dam and discuss the possibility that physically distinct events may have been previously grouped together under the slsn-i label. | spectra of hydrogen-poor superluminous supernovae from the palomar transient factory |
a significant fraction of stars between 7 and 11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. the answer depends critically on the rate of electron capture on 20ne in the degenerate oxygen-neon stellar core. however, because of the unknown strength of the transition between the ground states of 20ne and 20f, it has not previously been possible to fully constrain the rate. by measuring the transition, we establish that its strength is exceptionally large and that it enhances the capture rate by several orders of magnitude. this has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted by a thermonuclear explosion rather than collapsing to form a neutron star. importantly, our measurement resolves the last remaining nuclear physics uncertainty in the final evolution of degenerate oxygen-neon stellar cores, allowing future studies to address the critical role of convection, which at present is poorly understood. | discovery of an exceptionally strong β -decay transition of 20f and implications for the fate of intermediate-mass stars |
symbolic regression (sr) algorithms attempt to learn analytic expressions which fit data accurately and in a highly interpretable manner. conventional sr suffers from two fundamental issues which we address here. first, these methods search the space stochastically (typically using genetic programming) and hence do not necessarily find the best function. second, the criteria used to select the equation optimally balancing accuracy with simplicity have been variable and subjective. to address these issues we introduce exhaustive symbolic regression (esr), which systematically and efficiently considers all possible equations -- made with a given basis set of operators and up to a specified maximum complexity -- and is therefore guaranteed to find the true optimum (if parameters are perfectly optimised) and a complete function ranking subject to these constraints. we implement the minimum description length principle as a rigorous method for combining these preferences into a single objective. to illustrate the power of esr we apply it to a catalogue of cosmic chronometers and the pantheon+ sample of supernovae to learn the hubble rate as a function of redshift, finding $\sim$40 functions (out of 5.2 million trial functions) that fit the data more economically than the friedmann equation. these low-redshift data therefore do not uniquely prefer the expansion history of the standard model of cosmology. we make our code and full equation sets publicly available. | exhaustive symbolic regression |
massive stars (~8-25 m ⊙) stripped of their hydrogen-rich envelopes via binary interaction are thought to be the main progenitors for merging neutron stars and stripped-envelope supernovae. we recently presented the discovery of the first set of such stripped stars in a companion paper. here, we fit the spectra of 10 stars with new atmosphere models in order to constrain their stellar properties precisely. we find that the stellar properties align well with the theoretical expectations from binary evolution models for helium-core burning envelope-stripped stars. the fits confirm that the stars have high effective temperatures (t eff ~ 50-100 kk), high surface gravities ( $\mathrm{log}g\sim $ 5), and hydrogen-poor/helium-rich surfaces (x h,surf ~ 0-0.4) while showing for the first time a range of bolometric luminosities (103-105 l ⊙), small radii (~0.5-1 r ⊙), and low eddington factors (γ e~ 0.006-0.4). using these properties, we derive intermediate current masses (~1-8 m ⊙), which suggest that their progenitors were massive stars (~5-25 m ⊙) and that a subset will reach core-collapse, leaving behind neutron stars or black holes. using the model fits, we also estimate the emission rates of ionizing photons for these stars, which agree well with previous model expectations. further, by computing models for a range of mass-loss rates, we find that the stellar winds are weaker than predicted by any existing scheme ( ${\dot{m}}_{\mathrm{wind}}\lesssim {10}^{-9}$ m ⊙ yr-1). the properties of this first sample of intermediate-mass helium stars suggest they both contain progenitors of type ib and iib supernovae, and provide important benchmarks for binary evolution and population synthesis models. | stellar properties of observed stars stripped in binaries in the magellanic clouds |
gaussian processes (gp) provide an elegant and model-independent method for extracting cosmological information from the observational data. in this work, we employ gp to perform a joint analysis by using the geometrical cosmological probes such as supernova type ia (sn), cosmic chronometers (cc), baryon acoustic oscillations (bao), and the h0licow lenses sample to constrain the hubble constant h0, and reconstruct some properties of dark energy (de), viz., the equation of state parameter w, the sound speed of de perturbations cs2, and the ratio of de density evolution x =ρde/ρde ,0 . from the joint analysis sn+cc+bao+h0licow, we find that h0 is constrained at 1.1% precision with h0=73.78 ±0.84 kms-1mpc-1 , which is in agreement with sh0es and h0licow estimates, but in ∼6.2 σ tension with the current cmb measurements of h0. with regard to the de parameters, we find cs2<0 at ∼2 σ at high z, and the possibility of x to become negative for z >1.5 . we compare our results with the ones obtained in the literature, and discuss the consequences of our main results on the de theoretical framework. | measurements of h0 and reconstruction of the dark energy properties from a model-independent joint analysis |
a large fraction of gamma-ray burst (grb) lightcurves (lcs) show x-ray plateaus. we analyze all grbs with known redshifts presenting plateaus observed by the neil gehrels swift observatory from its launch until 2019 august. the fundamental plane relation between the rest-frame time and x-ray luminosity at the end of the plateau emission and the peak prompt luminosity holds for all the grb classes when selection biases and cosmological evolutions are applied. we have discovered two important findings: (1) a new class of long grbs with good data coverage: the platinum sample; and (2) the platinum, the sne-lgrb, and the kn-sgrb samples, yield the smallest intrinsic scatter with σplatinum,grb-sne = 0.22 ± 0.10 and σkn-sgrb = 0.24 ± 0.12. the sne-lgrbs are composed of grbs associated spectroscopically with the sne ib,c, the kn-sgrbs are composed by eight grbs associated with kilonovae or where there could have been such an association. the highest correlation coefficients are yielded for the sn-lgrb-abc sample, which includes grbs spectroscopically associated with sne ib/c or with a clear optical bump in the lc resembling the sne ib/c, ( ${r}_{\mathrm{sn} \mbox{-} \mathrm{lgrb} \mbox{-} \mathrm{abc}}^{2}=0.95$ ), the sn-lgrbs ( ${r}_{\mathrm{sn} \mbox{-} \mathrm{lgrb}}^{2}=0.91$ ), and the kn-sgrbs ( ${r}_{\mathrm{kn} \mbox{-} \mathrm{sgrb}}^{2}=0.90$ ) when the redshift evolution is considered. these category planes are reliable candidates to use as cosmological tools. furthermore, the distance from the gold fundamental plane is a crucial discriminant among classes. in fact, we find that the distributions of the distances of the sne-lgrb, sne-lgrb-abc, kn-sgrb, and sgrb samples from the gold fundamental plane are statistically different from the distribution of the gold grbs' distances from the gold fundamental plane with and without considering evolution cases. | the x-ray fundamental plane of the platinum sample, the kilonovae, and the sne ib/c associated with grbs |
the icecube report of a ∼ 3.5σ excess of 13 ± 5 neutrino events in the direction of the blazar txs 0506+056 in 2014-2015 and the 2017 detection of a high-energy neutrino event, icecube-170922a, during a gamma-ray flare from the same blazar, have revived the interest in scenarios for neutrino production in blazars. we perform comprehensive analyses on the long-term electromagnetic emission of txs 0506+056 using optical, x-ray, and gamma-ray data from the all-sky automated survey for supernovae, the neil gehrels swift observatory, monitor of all-sky x-ray image, and the fermi large area telescope. we also perform numerical modeling of the spectral energy distributions (seds) in four epochs prior to 2017 with contemporaneous gamma-ray and lower-energy (optical and/or x-ray) data. we find that the multi-epoch seds are consistent with a hybrid leptonic scenario, where the gamma-rays are produced in the blazar zone via external inverse compton scattering of accelerated electrons, and high-energy neutrinos are produced via the photomeson production process of co-accelerated protons. the multi-epoch seds can be satisfactorily explained with the same jet parameters and variable external photon density and electron luminosity. using the maximal neutrino flux derived for each epoch, we put an upper limit of ∼0.4-2 on the muon neutrino number in 10 years of icecube observations. our results are consistent with the icecube-170922a detection, which can be explained as an upper fluctuation from the average neutrino rate expected from the source, but in strong tension with the 2014-2015 neutrino flare. | multi-epoch modeling of txs 0506+056 and implications for long-term high-energy neutrino emission |
the most stringent local measurement of the hubble-lemaître constant from cepheid-calibrated type ia supernovae (sne ia) differs from the value inferred via the cosmic microwave background radiation (planck+λcdm) by ~5σ. this so-called hubble tension has been confirmed by other independent methods, and thus does not appear to be a possible consequence of systematic errors. here, we continue upon our prior work of using type ii supernovae to provide another, largely independent method to measure the hubble-lemaître constant. from 13 sne ii with geometric, cepheid, or tip of the red giant branch (trgb) host-galaxy distance measurements, we derive h$_0= 75.4^{+3.8}_{-3.7}$ km s-1 mpc-1 (statistical errors only), consistent with the local measurement but in disagreement by ~2.0σ with the planck+λcdm value. using only cepheids (n = 7), we find h$_0 = 77.6^{+5.2}_{-4.8}$ km s-1 mpc-1, while using only trgb (n = 5), we derive h$_0 = 73.1^{+5.7}_{-5.3}$ km s-1 mpc-1. via 13 variants of our data set, we derive a systematic uncertainty estimate of 1.5 km s-1 mpc-1. the median value derived from these variants differs by just 0.3 km s-1 mpc-1 from that produced by our fiducial model. because we only replace sne ia with sne ii - and we do not find statistically significant difference between the cepheid and trgb h0 measurements - our work reveals no indication that sne ia or cepheids could be the sources of the 'h0 tension.' we caution, however, that our conclusions rest upon a modest calibrator sample; as this sample grows in the future, our results should be verified. | a 5 per cent measurement of the hubble-lemaître constant from type ii supernovae |
comparing galactic chemical evolution models to the observed elemental abundances in the milky way, we show that neutron star mergers can be a leading r-process site only if at low metallicities such mergers have very short delay times and significant ejecta masses that are facilitated by the masses of the compact objects. namely, black hole-neutron star mergers, depending on the black hole spins, can play an important role in the early chemical enrichment of the milky way. we also show that none of the binary population synthesis models used in this letter, i.e., compas, startrack, brussels, combine, and bpass, can currently reproduce the elemental abundance observations. the predictions are problematic not only for neutron star mergers, but also for type ia supernovae, which may point to shortcomings in binary evolution models. | can neutron star mergers alone explain the r-process enrichment of the milky way? |
measurements of the h0 and σ8 parameters within the standard cosmological model recently highlighted significant statistical tensions between the cosmic microwave background and low-redshift probes, such as local distance ladder, weak lensing, and galaxy clustering surveys. in this work, we frame geometrical distances in a model-independent way by means of cosmographic approximations in the range z ∈(0 ,2.3 ) to take into account a robust dataset composed of baryon acoustic oscillations (baos), type ia supernovae (sn), cosmic chronometer (cc) data, and measurements from redshift space distortions (rsds). from the joint analysis bao +sn +cc +rsd , we find an accuracy of ∼1.4 % and ∼3.7 % on h0 and σ8, respectively. our result for h0 is at 2 σ tension with local measurements by the sh0es team, while our σ8 estimate is at 2.6 σ tension with planck-cmb analysis. this inference shows a tension statistically smaller when compared to those estimated via the lambda cold dark matter (λ cdm ) model. we also find that the jerk parameter can deviate more than 3 σ from the λ cdm prediction. under the same cosmographic setup, we also present results by considering a sh0es gaussian prior on h0 that allows for improved accuracy of the parameter space of the models. the present work brings observational constraints on h0 and σ8 into a new model-independent perspective, which differs from the predictions obtained within the λ cdm paradigm. | cosmographic view on the h0 and σ8 tensions |
context. type ib/c supernovae (sne ib/c) have been investigated in several single-object studies; however, there is still a paucity of works concerning larger, homogeneous samples of these hydrogen-poor transients, in particular regarding the premaximum phase of their light curves.aims: in this paper we present and analyze the early-time optical light curves (lcs, ugriz) of 20 sne ib/c from the sloan digital sky survey (sdss) sn survey ii, aiming to study their observational and physical properties, as well as to derive their progenitor parameters.methods: high-cadence, multiband lcs are fitted with a functional model and the best-fit parameters are compared among the sn types. bolometric lcs (blcs) are constructed for the entire sample. we also computed the black-body (bb) temperature (tbb) and photospheric radius (rph) evolution for each sn via bb fits on the spectral energy distributions. in addition, the bolometric properties are compared to both hydrodynamical and analytical model expectations.results: complementing our sample with literature data, we find that sne ic and ic-bl (broad-line) have shorter rise times than those of sne ib and iib. the decline rate parameter, δm15, is similar among the different subtypes. sne ic appear brighter and bluer than sne ib, but this difference vanishes if we consider host galaxy extinction corrections based on colors. templates for sn ib/c lcs are presented. our sne have typical tbb of ~10 000 k at the peak and rph of ~1015 cm. analysis of the blcs of sne ib and ic gives typical ejecta masses mej≈ 3.6-5.7 m⊙, energies ek≈ 1.5-1.7×1051 erg, and m(56ni) ≈ 0.3 m⊙. higher values for ek and m(56ni) are estimated for sne ic-bl (mej≈ 5.4 m⊙, ek≈ 10.7×1051 erg, m(56ni) ≈ 1.1 m⊙). for the majority of sne ic and ic-bl, we can put strong limits (<2-4 days) on the duration of the expected early-time plateau. less stringent limits can be placed on the duration of the plateau for the sample of sne ib. in the single case of sn ib 2006lc, a >5.9 days plateau seems to be detected. the rising part of the blcs is reproduced by power laws with index <2. for two events (sn 2005hm and sn 2007qx), we find signatures of a possible shock break-out cooling tail.conclusions: based on the limits for the plateau length and on the slow rise of the blcs, we find that in most of our sne ic and ic-bl the 56ni is mixed out to the outer layers, suggesting that sn ic progenitors are de facto helium poor. the derived progenitor parameters (56ni, ek, mej) are consistent with previous works. figures 1, 7 and tables 1-7 are available in electronic form at http://www.aanda.orglight curve templates are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/574/a60 | early-time light curves of type ib/c supernovae from the sdss-ii supernova survey |
we present the first three-dimensional (3d) simulation of the final minutes of iron core growth in a massive star, up to and including the point of core gravitational instability and collapse. we capture the development of strong convection driven by violent si burning in the shell surrounding the iron core. this convective burning builds the iron core to its critical mass and collapse ensues, driven by electron capture and photodisintegration. the non-spherical structure and motion generated by 3d convection is substantial at the point of collapse, with convective speeds of several hundreds of km s-1. we examine the impact of such physically realistic 3d initial conditions on the core-collapse supernova mechanism using 3d simulations including multispecies neutrino leakage and find that the enhanced post-shock turbulence resulting from 3d progenitor structure aids successful explosions. we conclude that non-spherical progenitor structure should not be ignored, and should have a significant and favorable impact on the likelihood for neutrino-driven explosions. in order to make simulating the 3d collapse of an iron core feasible, we were forced to make approximations to the nuclear network making this effort only a first step toward accurate, self-consistent 3d stellar evolution models of the end states of massive stars. | the three-dimensional evolution to core collapse of a massive star |
we present detailed chemical abundances for 99 red-giant branch stars in the centre of the sculptor dwarf spheroidal galaxy, which have been obtained from high-resolution vlt/flames spectroscopy. the abundances of li, na, α-elements (o, mg, si, ca ti), iron-peak elements (sc, cr, fe, co, ni, zn), and r- and s-process elements (ba, la, nd, eu) were all derived using stellar atmosphere models and semi-automated analysis techniques. the iron abundances populate the whole metallicity distribution of the galaxy with the exception of the very low metallicity tail, −2.3 ≤ [fe/h] ≤ −0.9. there is a marked decrease in [α/fe] over our sample, from the galactic halo plateau value at low [fe/h] and then, after a "knee", a decrease to sub-solar [α/fe] at high [fe/h]. this is consistent with products of core-collapse supernovae dominating at early times, followed by the onset of supernovae type ia as early as ∼12 gyr ago. the s-process products from low-mass agb stars also participate in the chemical evolution of sculptor on a timescale comparable to that of supernovae type ia. however, the r-process is consistent with having no time delay relative to core-collapse supernovae, at least at the later stages of the chemical evolution in sculptor. using the simple and well-behaved chemical evolution of sculptor, we further derive empirical constraints on the relative importance of massive stars and supernovae type ia to the nucleosynthesis of individual iron-peak and α-elements. the most important contribution of supernovae type ia is to the iron-peak elements: fe, cr, and mn. there is, however, also a modest but non-negligible contribution to both the heavier α-elements: s, ca and ti, and some of the iron-peak elements: sc and co. we see only a very small or no contribution to o, mg, ni, and zn from supernovae type ia in sculptor. the observed chemical abundances in sculptor show no evidence of a significantly different initial mass function, compared to that of the milky way. with the exception of neutron-capture elements at low [fe/h], the scatter around mean trends in sculptor for [fe/h] > −2.3 is extremely low, and compatible with observational errors. combined with the small scatter in the age-elemental abundances relation, this calls for an efficient mixing of metals in the gas in the centre of sculptor since ∼12 gyr ago. tables c.1-c.5 are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/626/a15 based on vlt/flames observations collected at the european organisation for astronomical research (eso) in the southern hemisphere under programmes 71.b-0641 and 171.b-0588. | vlt/flames high-resolution chemical abundances in sculptor: a textbook dwarf spheroidal galaxy |
we report on the energetics of molecular outflows in 14 local ultraluminous infrared galaxies (ulirgs) that show unambiguous outflow signatures (p cygni profiles or high-velocity absorption wings) in the far-infrared lines of oh measured with the herschel/pacs spectrometer. all sample galaxies are gas-rich mergers at various stages of the merging process. detection of both ground-state (at 119 and 79 μm) and one or more radiatively excited (at 65 and 84 μm) lines allows us to model the nuclear gas (≲300 pc) and the more extended components using spherically symmetric radiative transfer models. reliable models and the corresponding energetics are found in 12 of the 14 sources. the highest molecular outflow velocities are found in buried sources, in which slower but massive expansion of the nuclear gas is also observed. with the exception of a few outliers, the outflows have momentum fluxes of (2-5) × l ir/c and mechanical luminosities of (0.1-0.3)% of l ir. the moderate momentum boosts in these sources (≲3) suggest that the outflows are mostly momentum driven by the combined effects of active galactic nuclei (agns) and nuclear starbursts, as a result of radiation pressure, winds, and supernova remnants. in some sources (∼20%), however, powerful (1010.5-11 l ⊙) agn feedback and (partially) energy-conserving phases are required, with momentum boosts in the range of 3-20. these outflows appear to be stochastic, strong agn feedback events that occur throughout the merging process. in a few sources, the outflow activity in the innermost regions has subsided in the past ∼1 myr. while oh traces the molecular outflows at subkiloparsec scales, comparison of the masses traced by oh with those previously inferred from tracers of more extended outflowing gas suggests that most mass is loaded (with loading factors of \dot{m}/{sfr}=1{--}10) from the central galactic cores (a few × 100 pc), qualitatively consistent with an ongoing inside-out quenching of star formation. outflow depletion timescales are <108 yr, shorter than the gas consumption timescales by factors of 1.1-15, and are anticorrelated with the agn luminosity. | molecular outflows in local ulirgs: energetics from multitransition oh analysis |
the massive black hole (bh) population in dwarf galaxies (m bh ≲ 105 m ⊙) can provide strong constraints on the origin of bh seeds. however, traditional optical searches for active galactic nuclei (agns) only reliably detect high-accretion, relatively high-mass bhs in dwarf galaxies with low amounts of star formation, leaving a large portion of the overall bh population in dwarf galaxies relatively unexplored. here, we present a sample of 81 dwarf galaxies (m ⋆ ≤ 3 × 109 m ⊙) with detectable [fe x]λ6374 coronal line emission indicative of accretion onto massive bhs, only two of which were previously identified as optical agns. we analyze optical spectroscopy from the sloan digital sky survey and find [fe x]λ6374 luminosities in the range l [fe x] ≈ 1036-1039 erg s-1, with a median value of 1.6 × 1038 erg s-1. the [fe x] λ6374 luminosities are generally much too high to be produced by stellar sources, including luminous type iin supernovae (sne). moreover, based on known sne rates, we expect at most eight type iin sne in our sample. that said, the [fe x]λ6374 luminosities are consistent with accretion onto massive bhs from agns or tidal disruption events (tdes). we find additional indicators of bh accretion in some cases using other emission line diagnostics, optical variability, and x-ray and radio emission (or some combination of these). however, many of the galaxies in our sample only have evidence for a massive bh based on their [fe x]λ6374 luminosities. this work highlights the power of coronal line emission to find bhs in dwarf galaxies missed by other selection techniques and to probe the bh population in bluer, lower-mass dwarf galaxies. | a sample of massive black holes in dwarf galaxies detected via [fe x] coronal line emission: active galactic nuclei and/or tidal disruption events |
beyond-the-standard-model interactions of neutrinos among themselves—secret interactions—in the supernova core may prevent the shock revival, halting the supernova explosion. besides, if supernova neutrinos en route to earth undergo secret interactions with relic neutrinos, the neutrino burst reaching earth may be down-scattered in energy, falling below the detection threshold. we probe secret neutrino interactions through supernova neutrinos and apply our findings to the supernova sn 1987a. we place the most stringent bounds on flavor-universal secret interactions occurring through a new mediator with mass between 10 mev and 1 gev. | core-collapse supernovae stymie secret neutrino interactions |
the unprecedented volume and rate of transient events that will be discovered by the large synoptic survey telescope (lsst) demand that the astronomical community update its follow-up paradigm. alert-brokers—automated software system to sift through, characterize, annotate, and prioritize events for follow-up—will be critical tools for managing alert streams in the lsst era. the arizona-noao temporal analysis and response to events system (antares) is one such broker. in this work, we develop a machine learning pipeline to characterize and classify variable and transient sources only using the available multiband optical photometry. we describe three illustrative stages of the pipeline, serving the three goals of early, intermediate, and retrospective classification of alerts. the first takes the form of variable versus transient categorization, the second a multiclass typing of the combined variable and transient data set, and the third a purity-driven subtyping of a transient class. although several similar algorithms have proven themselves in simulations, we validate their performance on real observations for the first time. we quantitatively evaluate our pipeline on sparse, unevenly sampled, heteroskedastic data from various existing observational campaigns, and demonstrate very competitive classification performance. we describe our progress toward adapting the pipeline developed in this work into a real-time broker working on live alert streams from time-domain surveys. | machine-learning-based brokers for real-time classification of the lsst alert stream |
we propose a cosmological model, ü λ cdm , based on "über gravity," which is a canonical ensemble average of many theories of gravity. in this model, we have a sharp transition from (a purely) λ cdm era to a phase in which the ricci scalar is a constant. this transition occurs when the ricci scalar reaches a critical scale or alternatively a transition redshift, z⊕. we use the observations of baryonic acoustic oscillations and supernovae ia, as well as the cosmic microwave background data to constrain ü λ cdm . this yields h0=70.6-1.3+1.1 km /s /mpc , ωm=0.2861 ±0.0092 , and z⊕=0.53 7-0.375+0.277, providing a marginally better fit with a akaike information criterion of 0.8. therefore, ü λ cdm can ease the h0 tension, albeit marginally, with one additional free parameter. we also provide a preliminary study of the linear perturbation theory in ü λ cdm that points to interesting potential smoking guns in the observations of large scale structure at z <z⊕. | h0 tension as a hint for a transition in gravitational theory |
based on their relatively isolated environments, we argue that luminous blue variables (lbvs) must be primarily the product of binary evolution, challenging the traditional single-star view wherein lbvs mark a brief transition between massive o-type stars and wolf-rayet (wr) stars. if the latter were true, then lbvs should be concentrated in young massive clusters like early o-type stars. this is decidedly not the case. examining locations of lbvs in our galaxy and the magellanic clouds reveals that, with only a few exceptions, lbvs systematically avoid clusters of o-type stars. in the large magellanic cloud, lbvs are statistically much more isolated than o-type stars, and (perhaps most surprisingly) even more isolated than wr stars. this makes it impossible for lbvs to be single `massive stars in transition' to wr stars. instead, we propose that massive stars and supernova (sn) subtypes are dominated by bifurcated evolutionary paths in interacting binaries, wherein most wr stars and type ibc supernovae (sne ibc) correspond to the mass donors, while lbvs (and their lower mass analogues like b[e] supergiants, which are even more isolated) are the mass gainers. in this view, lbvs are evolved massive blue stragglers. through binary mass transfer, rejuvinated mass gainers get enriched, spun up, and sometimes kicked far from their clustered birth sites by their companion's sn. this scenario agrees better with lbvs exploding as sne iin in isolation, and it predicts that many massive runaway stars may be rapid rotators. mergers or blue thorne-zytkow-like objects might also give rise to lbvs, but these scenarios may have a harder time explaining why lbvs avoid clusters. | luminous blue variables are antisocial: their isolation implies that they are kicked mass gainers in binary evolution |
we present zwicky transient facility (ztf) observations of the tidal disruption flare at2018zr/ps18kh reported by holoien et al. and detected during ztf commissioning. the ztf light curve of the tidal disruption event (tde) samples the rise-to-peak exceptionally well, with 50 days of g- and r-band detections before the time of maximum light. we also present our multi-wavelength follow-up observations, including the detection of a thermal (kt ≈ 100 ev) x-ray source that is two orders of magnitude fainter than the contemporaneous optical/uv blackbody luminosity, and a stringent upper limit to the radio emission. we use observations of 128 known active galactic nuclei (agns) to assess the quality of the ztf astrometry, finding a median host-flare distance of 0.″2 for genuine nuclear flares. using ztf observations of variability from known agns and supernovae we show how these sources can be separated from tdes. a combination of light-curve shape, color, and location in the host galaxy can be used to select a clean tde sample from multi-band optical surveys such as ztf or the large synoptic survey telescope. | the first tidal disruption flare in ztf: from photometric selection to multi-wavelength characterization |
we present predictions for the gravitational wave (gw) emission of 3d supernova simulations performed for a 15 solar-mass progenitor with the prometheus-vertex code using energy-dependent, three-flavour neutrino transport. the progenitor adopted from stellar evolution calculations including magnetic fields had a fairly low specific angular momentum (jfe ≲ 1015 cm2 s-1) in the iron core (central angular velocity ωfe,c ∼ 0.2 rad s-1), which we compared to simulations without rotation and with artificially enhanced rotation (jfe ≲ 2 × 1016 cm2 s-1; ωfe,c ∼ 0.5 rad s-1). our results confirm that the time-domain gw signals of sne are stochastic, but possess deterministic components with characteristic patterns at low frequencies (≲200 hz), caused by mass motions due to the standing accretion shock instability (sasi), and at high frequencies, associated with gravity-mode oscillations in the surface layer of the proto-neutron star (pns). non-radial mass motions in the post-shock layer as well as pns convection are important triggers of gw emission, whose amplitude scales with the power of the hydrodynamic flows. there is no monotonic increase of the gw amplitude with rotation, but a clear correlation with the strength of sasi activity. our slowly rotating model is a fainter gw emitter than the non-rotating model because of weaker sasi activity and damped convection in the post-shock layer and pns. in contrast, the faster rotating model exhibits a powerful sasi spiral mode during its transition to explosion, producing the highest gw amplitudes with a distinctive drift of the low-frequency emission peak from ∼80-100 to ∼40-50 hz. this migration signifies shock expansion, whereas non-exploding models are discriminated by the opposite trend. | gravitational waves from 3d core-collapse supernova models: the impact of moderate progenitor rotation |
the wind driven by the intense neutrino emission from a protoneutron star (pns) is an important site for producing nuclei heavier than the fe group. because of certain features in the neutrino angular distributions, the so-called fast flavor oscillations may occur very close to the pns surface, effectively resetting the neutrino luminosities and energy spectra that drive the wind. using the unoscillated neutrino emission characteristics from two core-collapse supernova simulations representative of relevant progenitors at the lower and higher mass end, we study the potential effects of fast flavor oscillations on neutrino-driven winds and their nucleosynthesis. we find that such oscillations can increase the total mass loss by factors up to ∼1.5-1.7 and lead to significantly more proton-rich conditions. the latter effect can greatly enhance the production of 64zn and the so-called light p-nuclei 74se, 78kr, and 84sr. implications for abundances in metal-poor stars, galactic chemical evolution in general, and isotopic anomalies in meteorites are discussed. | potential impact of fast flavor oscillations on neutrino-driven winds and their nucleosynthesis |
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