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in core-collapse supernovae, the neutrino density is so large that neutrino flavor instabilities, leading to flavor conversion, can be triggered by the forward scattering of neutrinos among each other, if a crossing between the angular distributions of electron neutrino and antineutrinos exists (fast instability) or in the presence of perturbations induced by the neutrino vacuum frequency (slow instability). recently, it has been advanced the conjecture that neutrino collisions with the medium could be another mean to kickstart flavor change (collisional instability). we rely on a spherically symmetric core-collapse supernova model with mass $18.6\ m_\odot$, compute the neutrino angular distributions solving the kinetic equations and investigate the occurrence of flavor instabilities at different post-bounce times, ranging from the accretion phase to the early cooling phase. we find that fast and slow flavor instabilities largely dominate over the collisional ones in the decoupling region for all post-bounce times. while more work is needed to assess the relevance of collisional instabilities in neutrino-dense environments, our findings suggest that neutrino collisions with matter affect the flavor evolution in the decoupling region, but are not responsible for triggering flavor conversion. | do neutrinos become flavor unstable due to collisions with matter in the supernova decoupling region? |
star-forming galaxies are considered to be the leading candidate sources dominating cosmic reionization at z\gt 7: the search for analogs at moderate redshift showing lyman continuum (lyc) leakage is currently an active line of research. we have observed a star-forming galaxy at z = 3.2 with hubble/wfc3 in the f336w filter, corresponding to the 730-890 å rest-frame, and detected lyc emission. this galaxy is very compact and also has a large oxygen ratio [{{o}} {{iii}}]λ 5007/[{{o}} {{ii}}]λ 3727 (≳ 10). no nuclear activity is revealed from optical/near-infrared spectroscopy and deep multi-band photometry (including the 6 ms x-ray chandra observations). the measured escape fraction of ionizing radiation spans the range 50%-100%, depending on the intergalactic medium (igm) attenuation. the lyc emission is measured at {m}{{f}336{{w}}}=27.57+/- 0.11 (with signal-to-noise ratio (s/n) = 10) and is spatially unresolved, with an effective radius of {r}e\lt 200 pc. predictions from photoionization and radiative transfer models are in line with the properties reported here, indicating that stellar winds and supernova explosions in a nucleated star-forming region can blow cavities generating density-bounded conditions compatible to optically thin media. irrespective of the nature of the ionizing radiation, spectral signatures of these sources over the entire electromagnetic spectrum are of central importance for their identification during the epoch of reionization when the lyc is unobservable. intriguingly, the spitzer/irac photometric signature of intense rest-frame optical emissions ([o iii]λλ4959,5007 + hβ) recently observed at z≃ 7.5{--}8.5 is similar to what is observed in this galaxy. only the james webb space telescope will measure optical line ratios at z\gt 7, allowing a direct comparison with the lower-redshift lyc emitters, such as that reported here. based on observations made with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. these observations are associated with programs 9425, 11359, 12060, 12440, 14088. | hubble imaging of the ionizing radiation from a star-forming galaxy at z=3.2 with fesc>50% |
the growth of a supermassive black hole (bh) is determined by how much gas the host galaxy is able to feed it, which in turn is controlled by the cosmic environment, through galaxy mergers and accretion of cosmic flows that time how galaxies obtain their gas, and also by internal processes in the galaxy, such as star formation and feedback from stars and the bh itself. in this paper, we study the growth of a 1012 m⊙ halo at z = 2, which is the progenitor of a group of galaxies at z = 0, and of its central bh by means of a high-resolution zoomed cosmological simulation, the seth simulation. we study the evolution of the bh driven by the accretion of cold gas in the galaxy, and explore the efficiency of the feedback from supernovae (sne). for a relatively inefficient energy input from sne, the bh grows at the eddington rate from early times, and reaches self-regulation once it is massive enough. we find that at early cosmic times z > 3.5, efficient feedback from sne forbids the formation of a settled disc as well as the accumulation of dense cold gas in the vicinity of the bh and starves the central compact object. as the galaxy and its halo accumulate mass, they become able to confine the nuclear inflows provided by major mergers and the bh grows at a sustained near-to-eddington accretion rate. we argue that this mechanism should be ubiquitous amongst low-mass galaxies, corresponding to galaxies with a stellar mass below ≲ 109 m⊙ in our simulations. | black hole evolution - i. supernova-regulated black hole growth |
we present six epochs of optical spectropolarimetry of the type ii supernova (sn) 2023ixf ranging from ~2 to 15 days after the explosion. polarimetry was obtained with the kast double spectrograph on the shane 3 m telescope at lick observatory, representing the earliest such observations ever captured for an sn. we observe a high continuum polarization p cont ≈ 1% on days +1.4 and +2.5 before dropping to 0.5% on day +3.5, persisting at that level up to day +14.5. remarkably, this change coincides temporally with the disappearance of highly ionized "flash" features. the decrease of the continuum polarization is accompanied by a ~70° rotation of the polarization position angle (pa) as seen across the continuum. the early evolution of the polarization may indicate different geometric configurations of the electron-scattering atmosphere as seen before and after the disappearance of the emission lines associated with highly ionized species (e.g., he ii, c iv, and n iii), which are likely produced by elevated mass loss shortly prior to the sn explosion. we interpret the rapid change of polarization and pa from days +2.5 to +4.5 as the time when the sn ejecta emerge from the dense asymmetric circumstellar material (csm). the temporal evolution of the continuum polarization and the pa is consistent with an aspherical sn explosion that exhibits a distinct geometry compared to the csm. the rapid follow-up spectropolarimetry of sn 2023ixf during the shock ionization phase reveals an exceptionally asymmetric mass-loss process leading up to the explosion. | early time spectropolarimetry of the aspherical type ii supernova sn 2023ixf |
the recent supernova, sn 2023ixf, one of the closest observed type ii sne has revealed the presence of a dense circumstellar material (csm). interaction of the sn ejecta with this dense csm may create high energy protons of pev energies through shock acceleration. these accelerated protons then colliding with the csm (inelastic $pp$ collision) can produce secondaries such as high energy gamma-rays and neutrinos. however, no gamma-rays and neutrinos have been detected by fermi-lat and icecube from this event. indeed, fermi-lat has placed an upper limits on the gamma-ray flux above $100$~mev to be $2.6 \times 10^{-11}~\rm erg~cm^{-2}~s^{-1}$. on the other hand icecube's upper limit on muon neutrino flux is $7.3\times 10^{-2} ~\rm gev~cm^{-2}$. using these experimental constraints and shock-csm properties derived from observations, we obtain new upper limits on the gamma-ray ($10^{-11}~\rm erg~cm^{-2}~s^{-1}$) and neutrino ($10^{-3}~\rm gev~cm^{-2}$) fluxes from sn 2023ixf produced via the $pp$ interaction channel. while we found the gamma-ray flux to be consistent with fermi-lat's upper limit, the neutrino flux is found to be about $2$ order smaller than the icecube's upper limit. we further analyse detection prospects of such secondary signals from future sn 2023 like events with upcoming detectors, cta and icecube-gen2 and found to have great discovery potential, if any event occurs within $7$ mpc. | new constraints on the gamma-ray and high energy neutrino fluxes from the circumstellar interaction of sn 2023ixf |
the hydrogen-rich outer layers of massive stars can be removed by interactions with a binary companion. theoretical models predict that this stripping produces a population of hot helium stars of ~2 to 8 solar masses (m☉), however, only one such system has been identified thus far. we used ultraviolet photometry to identify potential stripped helium stars then investigated 25 of them using optical spectroscopy. we identified stars with high temperatures (~60,000 to 100,000 kelvin), high surface gravities, and hydrogen-depleted surfaces; 16 stars also showed binary motion. these properties match expectations for stars with initial masses of 8 to 25 m☉ that were stripped by binary interaction. their masses fall in the gap between subdwarf helium stars and wolf-rayet stars. we propose that these stars could be progenitors of stripped-envelope supernovae. | an observed population of intermediate-mass helium stars that have been stripped in binaries |
we quantify the cosmological spread of baryons relative to their initial neighboring dark matter distribution using thousands of state-of-the-art simulations from the cosmology and astrophysics with machine learning simulations (camels) project. we show that dark matter particles spread relative to their initial neighboring distribution owing to chaotic gravitational dynamics on spatial scales comparable to their host dark matter halo. in contrast, gas in hydrodynamic simulations spreads much further from the initial neighboring dark matter owing to feedback from supernovae (sne) and active galactic nuclei (agn). we show that large-scale baryon spread is very sensitive to model implementation details, with the fiducial \textsc{simba} model spreading $\sim$40\% of baryons $>$1\,mpc away compared to $\sim$10\% for the illustristng and \textsc{astrid} models. increasing the efficiency of agn-driven outflows greatly increases baryon spread while increasing the strength of sne-driven winds can decrease spreading due to non-linear coupling of stellar and agn feedback. we compare total matter power spectra between hydrodynamic and paired $n$-body simulations and demonstrate that the baryonic spread metric broadly captures the global impact of feedback on matter clustering over variations of cosmological and astrophysical parameters, initial conditions, and galaxy formation models. using symbolic regression, we find a function that reproduces the suppression of power by feedback as a function of wave number ($k$) and baryonic spread up to $k \sim 10\,h$\,mpc$^{-1}$ while highlighting the challenge of developing models robust to variations in galaxy formation physics implementation. | cosmological baryon spread and impact on matter clustering in camels |
long-duration γ-ray bursts (grbs) accompany the collapse of massive stars and carry information about the central engine. however, no 3d models have been able to follow these jets from their birth via black hole (bh) to the photosphere. we present the first such 3d general-relativity magnetohydrodynamic simulations, which span over six orders of magnitude in space and time. the collapsing stellar envelope forms an accretion disk, which drags inwardly the magnetic flux that accumulates around the bh, becomes dynamically important, and launches bipolar jets. the jets reach the photosphere at ~1012 cm with an opening angle θj~ 6° and a lorentz factor γ j≲ 30, unbinding ≳90% of the star. we find that (i) the disk-jet system spontaneously develops misalignment relative to the bh rotational axis. as a result, the jet wobbles with an angle θt~ 12°, which can naturally explain quiescent times in grb lightcurves. the effective opening angle for detection θj+ θtsuggests that the intrinsic grb rate is lower by an order of magnitude than standard estimates. this suggests that successful grbs are rarer than currently thought and emerge in only ~0.1% of supernovae ib/c, implying that jets are either not launched or choked inside most supernova ib/c progenitors. (ii) the magnetic energy in the jet decreases due to mixing with the star, resulting in jets with a hybrid composition of magnetic and thermal components at the photosphere, where ~10% of the gas maintains magnetization σ ≳ 0.1. this indicates that both a photospheric component and reconnection may play a role in the prompt emission. | black hole to photosphere: 3d grmhd simulations of collapsars reveal wobbling and hybrid composition jets |
giant molecular clouds (gmcs) and their stellar offspring are the building blocks of galaxies. the physical characteristics of gmcs and their evolution are tightly connected to galaxy evolution. the macroscopic properties of the interstellar medium propagate into the properties of gmcs condensing out of it, with correlations between e.g. the galactic and gmc scale gas pressures, surface densities and volume densities. that way, the galactic environment sets the initial conditions for star formation within gmcs. after the onset of massive star formation, stellar feedback from e.g. photoionisation, stellar winds, and supernovae eventually contributes to dispersing the parent cloud, depositing energy, momentum and metals into the surrounding medium, thereby changing the properties of galaxies. this cycling of matter between gas and stars, governed by star formation and feedback, is therefore a major driver of galaxy evolution. much of the recent debate has focused on the durations of the various evolutionary phases that constitute this cycle in galaxies, and what these can teach us about the physical mechanisms driving the cycle. we review results from observational, theoretical, and numerical work to build a dynamical picture of the evolutionary lifecycle of gmc evolution, star formation, and feedback in galaxies. | the molecular cloud lifecycle |
we make a strong case that the fast neutrino-flavor conversion, one of the collective flavor oscillation modes, commonly occurs in core-collapse supernovae (ccsns). it is confirmed in the numerical data obtained in realistic simulations of ccsns, but the argument is much more generic and applicable universally: the coherent neutrino-nucleus scattering makes the electron lepton number (eln) change sign at some inward direction and trigger the flavor conversion in the outward direction in the preshock region. although the eln crossing is tiny and that is why it has eluded recognition so far, it is still large enough to induce the flavor conversion. our findings may have important observational consequences for ccsn neutrinos. | fast neutrino-flavor conversion in the preshock region of core-collapse supernovae |
we study the cosmological constant (λ ) in the standard λ cold dark matter model by introducing the graduated dark energy (gde) characterized by a minimal dynamical deviation from the null inertial mass density of the λ in the form ρinert∝ρλ<0 with λ <1 being a ratio of two odd integers, for which its energy density ρ dynamically takes negative values in the finite past. for large negative values of λ , it creates a phenomenological model described by a smooth function that approximately describes the λ spontaneously switching sign in the late universe to become positive today. we confront the model with the latest combined observational datasets of planck +baryon acoustic oscillations +supernova +h . it is striking that the data predict bimodal posterior probability distributions for the parameters of the model along with large negative λ values; the new maximum significantly excludes the λ , and the old maximum contains the λ . the improvement in the goodness of fit for the λ reaches highly significant levels, δ χmin2=6.4 , for the new maxima, while it remains at insignificant levels, δ χmin2≲0.02 , for the old maxima. we show that, in contrast to the old maxima, which do not distinguish from the λ , the new maxima agree with the model-independent h0 measurements, high-precision ly -α data, and model-independent o m h2 diagnostic estimates. our results provide strong hints of a spontaneous sign switch in the cosmological constant and lead us to conjecture that the universe has transitioned from anti-de sitter vacua to de sitter vacua, at a redshift z ≈2.32 , and triggered the late-time acceleration, and suggests looking for such mechanisms in string theory constructions. | graduated dark energy: observational hints of a spontaneous sign switch in the cosmological constant |
supernovae (sne) embedded in dense circumstellar material (csm) may show prominent emission lines in their early-time spectra (≤10 days after the explosion), owing to recombination of the csm ionized by the shock-breakout flash. from such spectra (“flash spectroscopy”), we can measure various physical properties of the csm, as well as the mass-loss rate of the progenitor during the year prior to its explosion. searching through the palomar transient factory (ptf and iptf) sn spectroscopy databases from 2009 through 2014, we found 12 sne ii showing flash-ionized (fi) signatures in their first spectra. all are younger than 10 days. these events constitute 14% of all 84 sne in our sample having a spectrum within 10 days from explosion, and 18% of sne ii observed at ages <5 days, thereby setting lower limits on the fraction of fi events. we classified as “blue/featureless” (bf) those events having a first spectrum that is similar to that of a blackbody, without any emission or absorption signatures. it is possible that some bf events had fi signatures at an earlier phase than observed, or that they lack dense csm around the progenitor. within 2 days after explosion, 8 out of 11 sne in our sample are either bf events or show fi signatures. interestingly, we found that 19 out of 21 sne brighter than an absolute magnitude mr = -18.2 belong to the fi or bf groups, and that all fi events peaked above mr = -17.6 mag, significantly brighter than average sne ii. | flash spectroscopy: emission lines from the ionized circumstellar material around <10-day-old type ii supernovae |
we present ground-based and swift photometric and spectroscopic observations of the tidal disruption event (tde) asassn-15oi, discovered at the centre of 2masx j20390918-3045201 (d ≃ 216 mpc) by the all-sky automated survey for supernovae. the source peaked at a bolometric luminosity of l ≃ 1.3 × 1044 erg s-1 and radiated a total energy of e ≃ 6.6 × 1050 erg over the first ∼3.5 months of observations. the early optical/uv emission of the source can be fit by a blackbody with temperature increasing from t ∼ 2 × 104 k to t ∼ 4 × 104 k while the luminosity declines from l ≃ 1.3 × 1044 erg s-1 to l ≃ 2.3 × 1043 erg s-1, requiring the photosphere to be shrinking rapidly. the optical/uv luminosity decline during this period is most consistent with an exponential decline, l∝ e^{-(t-t_0)/τ}, with τ ≃ 46.5 d for t0 ≃ 57241.6 (mjd), while a power-law decline of l ∝ (t - t0)-α with t0 ≃ 57 212.3 and α = 1.62 provides a moderately worse fit. asassn-15oi also exhibits roughly constant soft x-ray emission that is significantly weaker than the optical/uv emission. spectra of the source show broad helium emission lines and strong blue continuum emission in early epochs, although these features fade rapidly and are not present ∼3 months after discovery. the early spectroscopic features and colour evolution of asassn-15oi are consistent with a tde, but the rapid spectral evolution is unique among optically selected tdes. | asassn-15oi: a rapidly evolving, luminous tidal disruption event at 216 mpc |
current time domain facilities are discovering hundreds of new galactic and extra-galactic transients every week. classifying the ever-increasing number of transients is challenging, yet crucial to furthering our understanding of their nature, discovering new classes, and ensuring sample purity, for instance, for supernova ia cosmology. the zwicky transient facility is one example of such a survey. in addition, it has a dedicated very-low resolution spectrograph, the sedmachine, operating on the palomar 60-inch telescope. this spectrograph's primary aim is object classification. in practice most, if not all, transients of interest brighter than ∼19 mag are typed. this corresponds to approximately 10-15 targets a night. in this paper, we present a fully automated pipeline for the sedmachine. this pipeline has been designed to be fast, robust, stable and extremely flexible. pysedm enables the fully automated spectral extraction of a targeted point source object in less than five minutes after the end of the exposure. the spectral color calibration is accurate at the few percent level. in the 19 weeks since pysedm entered production in early august of 2018, we have classified, among other objects, about 400 type ia supernovae and 140 type ii supernovae. we conclude that low resolution, fully automated spectrographs such as the "sedmachine with pysedm" installed on 2-m class telescopes within the southern hemisphere could allow us to automatically and simultaneously type and obtain a redshift for most (if not all) bright transients detected by lsst within z < 0.2, notably potentially all type ia supernovae. in comparison with the current sedm design, this would require higher spectral resolution (r ≳ 1000) and slightly improved throughput. with this perspective in mind, pysedm is designed to easily be adaptable to any ifu-like spectrograph. https://github.com/mickaelrigault/pysedm | fully automated integral field spectrograph pipeline for the sedmachine: pysedm |
we analyse the f(r) gravity in the so-called jordan frame, as implemented to the isotropic universe dynamics. the goal of the present study is to show that according to recent data analyses of the supernovae ia pantheon sample, it is possible to account for an effective redshift dependence of the hubble constant. this is achieved via the dynamics of a non-minimally coupled scalar field, as it emerges in the f(r) gravity. we face the question both from an analytical and purely numerical point of view, following the same technical paradigm. we arrive to establish that the expected decay of the hubble constant with the redshift z is ensured by a form of the scalar field potential, which remains essentially constant for z ≲ 0.3, independently if this request is made a priori, as in the analytical approach, or obtained a posteriori, when the numerical procedure is addressed. thus, we demonstrate that an f(r) dark energy model is able to account for an apparent variation of the hubble constant due to the rescaling of the einstein constant by the f(r) scalar mode. | f(r) gravity in the jordan frame as a paradigm for the hubble tension |
we examine nucleosynthesis in the innermost neutrino-processed ejecta (a few {10}-3 {m}⊙ ) of self-consistent two-dimensional explosion models of core-collapse supernovae (ccsne) for six progenitor stars with different initial masses. three models have initial masses near the low-mass end of the sn range of 8.8 {m}⊙(e8.8; electron-capture sn), 9.6 {m}⊙(z9.6), and 8.1 {m}⊙(u8.1), with initial metallicities of 1, 0, and 10-4 times the solar metallicity, respectively. the other three are solar-metallicity models with initial masses of 11.2 {m}⊙(s11), 15 {m}⊙(s15), and 27 {m}⊙(s27). the low-mass models e8.8, z9.6, and u8.1 exhibit high production factors (nucleosynthetic abundances relative to the solar abundances) of 100-200 for light trans-fe elements from zn to zr. this is associated with an appreciable ejection of neutron-rich matter in these models. remarkably, the nucleosynthetic outcomes for the progenitors e8.8 and z9.6 are almost identical, including interesting productions of 48ca and 60fe, irrespective of their quite different (o-ne-mg and fe) cores prior to collapse. in the more massive models s11, s15, and s27, several proton-rich isotopes of light trans-fe elements including the p-isotope 92mo (for s27) are made, up to production factors of ∼30. both electron-capture sne and ccsne near the low-mass end can therefore be dominant contributors to the galactic inventory of light trans-fe elements from zn to zr and probably 48ca and live 60fe. the innermost ejecta of more massive sne may have only subdominant contributions to the chemical enrichment of the galaxy except for 92mo. | nucleosynthesis in the innermost ejecta of neutrino-driven supernova explosions in two dimensions |
we use three-dimensional hydrodynamic simulations of vertically stratified patches of galactic discs to study how the spatio-temporal clustering of supernovae (sne) enhances the power of galactic winds. randomly distributed sne drive inefficient galactic winds because most supernova remnants lose their energy radiatively before breaking out of the disc. accounting for the fact that most star formation is clustered alleviates this problem. superbubbles driven by the combined effects of clustered sne propagate rapidly enough to break out of galactic discs well before the clusters' sne stop going off. the radiative losses post-breakout are reduced dramatically and a large fraction (≳0.2) of the energy released by sne vents into the halo powering a strong galactic wind. these energetic winds are capable of providing strong preventative feedback and eject substantial mass from the galaxy with outflow rates of the order of the star formation rate. the momentum flux in the wind is only of order that injected by the sne, because the hot gas vents before doing significant work on the surroundings. we show that our conclusions hold for a range of galaxy properties, both in the local universe (e.g. m82) and at high redshift (e.g. z ∼ 2 star-forming galaxies). we further show that if the efficiency of forming star clusters increases with increasing gas surface density, as suggested by theoretical arguments, the condition for star cluster-driven superbubbles to break out of galactic discs corresponds to a threshold star formation rate surface density for the onset of galactic winds {∼ } 0.03 m_⊙ yr^{-1} kpc^{-2}, of order that observed. | clustered supernovae drive powerful galactic winds after superbubble breakout |
we present observations of ps16dtm (also known as sn 2016ezh), a luminous transient that occurred at the nucleus of a narrow-line seyfert 1 galaxy hosting a 106 m ⊙ black hole. the light curve shows that ps16dtm exhibited a plateau phase for ∼100 days, during which it showed no color evolution, maintained a blackbody temperature of ∼ 1.7× {10}4 k, and radiated at approximately the eddington luminosity of the supermassive black hole (smbh). the spectra exhibit multicomponent hydrogen emission lines and strong fe ii emission, show little time evolution, and closely resemble the spectra of nls1s while being distinct from those of type iin supernovae (sne iin). moreover, ps16dtm is undetected in the x-rays to a limit an order of magnitude below an archival x-ray detection of its host galaxy. these observations strongly link ps16dtm to activity associated with the smbh and are difficult to reconcile with an sn origin or known forms of active galactic nucleus (agn) variability. therefore, we argue that ps16dtm is a tidal disruption event (tde) in which the accretion of the stellar debris powers the rise in the continuum and excitation of the preexisting broad-line region, while obscuring the x-ray-emitting region of the preexisting agn disk. we predict that ps16dtm will remain bright for years and that the x-ray emission will reappear on a similar timescale as the accretion rate declines. placing ps16dtm in the context of other tdes, we find that tdes in agn galaxies are more efficient and reach eddington luminosities, likely due to interaction of the stellar debris with the preexisting accretion disk. | ps16dtm: a tidal disruption event in a narrow-line seyfert 1 galaxy |
the present work is based on a parametric reconstruction of the deceleration parameter q( z) in a model for the spatially flat frw universe filled with dark energy and non-relativistic matter. in cosmology, the parametric reconstruction technique deals with an attempt to build up a model by choosing some specific evolution scenario for a cosmological parameter and then estimate the values of the parameters with the help of different observational datasets. in this paper, we have proposed a logarithmic parametrization of q( z) to probe the evolution history of the universe. using the type ia supernova, baryon acoustic oscillation and the cosmic microwave background datasets, the constraints on the arbitrary model parameters q0 and q1 are obtained (within 1σ and 2σ confidence limits) by χ 2-minimization technique. we have then reconstructed the deceleration parameter, the total eos parameter ω _tot, the jerk parameter and have compared the reconstructed results of q( z) with other well-known parametrizations of q( z). we have also shown that two model selection criteria (namely, the akaike information criterion and bayesian information criterion) provide a clear indication that our reconstructed model is well consistent with other popular models. | a parametric reconstruction of the deceleration parameter |
we present the results of a search for rapidly evolving transients in the dark energy survey supernova programme. these events are characterized by fast light-curve evolution (rise to peak in ≲10 d and exponential decline in ≲30 d after peak). we discovered 72 events, including 37 transients with a spectroscopic redshift from host galaxy spectral features. the 37 events increase the total number of rapid optical transients by more than a factor of two. they are found at a wide range of redshifts (0.05 < z < 1.56) and peak brightnesses (-15.75 > mg > -22.25). the multiband photometry is well fit by a blackbody up to few weeks after peak. the events appear to be hot (t ≈ 10 000-30 000 k) and large (r ≈ 1014 - 2 × 1015 cm) at peak, and generally expand and cool in time, though some events show evidence for a receding photosphere with roughly constant temperature. spectra taken around peak are dominated by a blue featureless continuum consistent with hot, optically thick ejecta. we compare our events with a previously suggested physical scenario involving shock breakout in an optically thick wind surrounding a core-collapse supernova, we conclude that current models for such a scenario might need an additional power source to describe the exponential decline. we find that these transients tend to favour star-forming host galaxies, which could be consistent with a core-collapse origin. however, more detailed modelling of the light curves is necessary to determine their physical origin. | rapidly evolving transients in the dark energy survey |
we study the merger of binary neutron stars using different realistic, microphysical nuclear equations of state, as well as incorporating magnetic field and neutrino cooling effects. in particular, we concentrate on the influence of the equation of state on the gravitational wave signature and also on its role, in combination with cooling and electromagnetic effects, in determining the properties of the hypermassive neutron star resulting from the merger, the production of neutrinos, and the characteristics of ejecta from the system. the ejecta we find are consistent with other recent studies that find soft equations of state produce more ejecta than stiffer equations of state. moreover, the degree of neutron richness increases for softer equations of state. in light of reported kilonova observations (associated to grb 130603b and grb 060614) and the discovery of relatively low abundances of heavy, radioactive elements in deep sea deposits (with respect to possible production via supernovae), we speculate that a soft equation of state (eos) might be preferred—because of its significant production of sufficiently neutron rich ejecta—if such events are driven by binary neutron star mergers. we also find that realistic magnetic field strengths, obtained with a subgrid model tuned to capture magnetic amplification via the kelvin-helmholtz instability at merger, are generally too weak to affect the gravitational wave signature postmerger within a time scale of ≈10 ms but can have subtle effects on the postmerger dynamics. | effects of the microphysical equation of state in the mergers of magnetized neutron stars with neutrino cooling |
we conduct precise strong lensing mass modeling of four hubble frontier field (hff) clusters, abell 2744, macs j0416.1-2403, macs j0717.5+3745, and macs j1149.6+2223, for which hff imaging observations are completed. we construct a refined sample of more than 100 multiple images for each cluster by taking advantage of the full-depth hff images, and conduct mass modeling using the glafic software, which assumes simply parametrized mass distributions. our mass modeling also exploits a magnification constraint from the lensed sn ia hff14tom for abell 2744 and positional constraints from the multiple images s1-s4 of the lensed supernova sn refsdal for macs j1149.6+2223. we find that our best-fitting mass models reproduce the observed image positions with rms errors of ∼0.″4, which are smaller than rms errors in previous mass modeling that adopted similar numbers of multiple images. our model predicts a new image of sn refsdal with a relative time delay and magnification that are fully consistent with a recent detection of reappearance. we then construct catalogs of z ∼ 6-9 dropout galaxies behind the four clusters and estimate magnification factors for these dropout galaxies with our best-fitting mass models. the dropout sample from the four cluster fields contains ∼120 galaxies at z ≳ 6, about 20 of which are predicted to be magnified by a factor of more than 10. some of the high-redshift galaxies detected in the hff have lensing-corrected magnitudes of muv ∼ -15 to -14. our analysis demonstrates that the hff data indeed offer an ideal opportunity to study faint high-redshift galaxies. all lensing maps produced from our mass modeling will be made available on the space telescope science institute website (https://archive.stsci.edu/prepds/frontier/lensmodels/). | precise strong lensing mass modeling of four hubble frontier field clusters and a sample of magnified high-redshift galaxies |
we present multi-wavelength observations of sn 2014c during the first 500 days. these observations represent the first solid detection of a young extragalactic stripped-envelope sn out to high-energy x-rays ∼40 kev. sn 2014c shows ordinary explosion parameters (ek ∼ 1.8 × 1051 erg and mej ∼ 1.7 m⊙). however, over an ∼1 year timescale, sn 2014c evolved from an ordinary hydrogen-poor supernova into a strongly interacting, hydrogen-rich supernova, violating the traditional classification scheme of type-i versus type-ii sne. signatures of the sn shock interaction with a dense medium are observed across the spectrum, from radio to hard x-rays, and revealed the presence of a massive shell of ∼1 m⊙ of hydrogen-rich material at ∼6 × 1016 cm. the shell was ejected by the progenitor star in the decades to centuries before collapse. this result challenges current theories of massive star evolution, as it requires a physical mechanism responsible for the ejection of the deepest hydrogen layer of h-poor sn progenitors synchronized with the onset of stellar collapse. theoretical investigations point at binary interactions and/or instabilities during the last nuclear burning stages as potential triggers of the highly time-dependent mass loss. we constrain these scenarios utilizing the sample of 183 sne ib/c with public radio observations. our analysis identifies sn 2014c-like signatures in ∼10% of sne. this fraction is reasonably consistent with the expectation from the theory of recent envelope ejection due to binary evolution if the ejected material can survive in the close environment for 103-104 years. alternatively, nuclear burning instabilities extending to core c-burning might play a critical role. | ejection of the massive hydrogen-rich envelope timed with the collapse of the stripped sn 2014c |
the synthesis of nuclei in diverse cosmic scenarios is reviewed, with a summary of the basic concepts involved before a discussion of the current status in each case is made. we review the physics of the early universe, the proton to neutron ratio influence in the observed helium abundance, reaction networks, the formation of elements up to beryllium, the inhomogeneous big bang model, and the big bang nucleosynthesis constraints on cosmological models. attention is paid to element production in stars, together with the details of the pp chain, the pp reaction, 3he formation and destruction, electron capture on 7be, the importance of 8b formation and its relation to solar neutrinos, and neutrino oscillations. nucleosynthesis in massive stars is also reviewed, with focus on the cno cycle and its hot companion cycle, the rp-process, triple- α capture, and red giants and agb stars. the stellar burning of carbon, neon, oxygen, and silicon is presented in a separate section, as well as the slow and rapid nucleon capture processes and the importance of medium modifications due to electrons also for pycnonuclear reactions. the nucleosynthesis in cataclysmic events such as in novae, x-ray bursters and in core-collapse supernovae, the role of neutrinos, and the supernova radioactivity and light-curve is further discussed, as well as the structure of neutron stars and its equation of state. a brief review of the element composition found in cosmic rays is made in the end. | frontiers in nuclear astrophysics |
we present ztf18abvkwla (the "koala"), a fast blue optical transient discovered in the zwicky transient facility (ztf) one-day cadence (1dc) survey. ztf18abvkwla has a number of features in common with the groundbreaking transient at 2018cow: blue colors at peak ( $g-r\approx -0.5$ mag), a short rise time from half-max of under two days, a decay time to half-max of only three days, a high optical luminosity ( ${m}_{g,\mathrm{peak}}\approx -20.6$ mag), a hot (≳40,000 k) featureless spectrum at peak light, and a luminous radio counterpart. at late times ( ${\rm{\delta }}t\gt 80\,\mathrm{days}$ ), the radio luminosity of ztf18abvkwla ( $\nu {l}_{\nu }\gtrsim {10}^{40}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ at 10 $\mathrm{ghz}$ , observer-frame) is most similar to that of long-duration gamma-ray bursts (grbs). the host galaxy is a dwarf starburst galaxy ( $m\approx 5\times {10}^{8}\,{m}_{\odot }$ , $\mathrm{sfr}\approx 7\,{m}_{\odot }\,{\mathrm{yr}}^{-1}$ ) that is moderately metal-enriched ( $\mathrm{log}[{\rm{o}}/{\rm{h}}]\approx 8.5$ ), similar to the hosts of grbs and superluminous supernovae. as in at2018cow, the radio and optical emission in ztf18abvkwla likely arise from two separate components: the radio from fast-moving ejecta ( ${\rm{\gamma }}\beta c\gt 0.38c$ ) and the optical from shock-interaction with confined dense material (<0.07 m⊙ in $\sim {10}^{15}\,\mathrm{cm}$ ). compiling transients in the literature with ${t}_{\mathrm{rise}}\lt 5\,\mathrm{days}$ and ${m}_{\mathrm{peak}}\lt -20$ mag, we find that a significant number are engine-powered, and suggest that the high peak optical luminosity is directly related to the presence of this engine. from 18 months of the 1dc survey, we find that transients in this rise-luminosity phase space are at least two to three orders of magnitude less common than cc sne. finally, we discuss strategies for identifying such events with future facilities like the large synoptic survey telescope, as well as prospects for detecting accompanying x-ray and radio emission. | the koala: a fast blue optical transient with luminous radio emission from a starburst dwarf galaxy at z = 0.27 |
the many unusual properties of the enigmatic at2018cow suggested that at least some subset of the empirical class of fast blue optical transients (fbots) represents a genuinely new astrophysical phenomenon. unfortunately, the intrinsic rarity and fleeting nature of these events have made it difficult to identify additional examples early enough to acquire the observations necessary to constrain theoretical models. we present here the zwicky transient facility discovery of at2020xnd (ztf20acigmel, the 'camel') at z = 0.243, the first unambiguous at2018cow analogue to be found and confirmed in real time. at2018cow and at2020xnd share all key observational properties: a fast optical rise, sustained high photospheric temperature, absence of a second peak attributable to ejection of a radioactively heated stellar envelope, extremely luminous radio, millimetre, and x-ray emission, and a dwarf-galaxy host. this supports the argument that at2018cow-like events represent a distinct phenomenon from slower-evolving radio-quiet supernovae, likely requiring a different progenitor or a different central engine. the sample properties of the four known members of this class to date disfavour tidal disruption models but are consistent with the alternative model of an accretion powered jet following the direct collapse of a massive star to a black hole. contextual filtering of alert streams combined with rapid photometric verification using multiband imaging provides an efficient way to identify future members of this class, even at high redshift. | real-time discovery of at2020xnd: a fast, luminous ultraviolet transient with minimal radioactive ejecta |
we return to interpreting the historical sn 1987a neutrino data from a modern perspective. to this end, we construct a suite of spherically symmetric supernova models with the prometheus-vertex code, using four different equations of state and five choices of final baryonic neutron-star (ns) mass in the 1.36 - 1.93 m⊙ range. our models include muons and proto-neutron star (pns) convection by a mixing-length approximation. the time-integrated signals of our 1.44 m⊙ models agree reasonably well with the combined data of the four relevant experiments, imb, kam-ii, bust, and lsd, but the high-threshold imb detector alone favors a ns mass of 1.7 - 1.8 m⊙ , whereas kam-ii alone prefers a mass around 1.4 m⊙ . the cumulative energy distributions in these two detectors are well-matched by models for such ns masses, and the previous tension between predicted mean neutrino energies and the combined measurements is gone, with and without flavor swap. generally, our predicted signals do not strongly depend on assumptions about flavor mixing, because the pns flux spectra depend only weakly on antineutrino flavor. while our models show compatibility with the events detected during the first seconds, pns convection and nucleon correlations in the neutrino opacities lead to short pns cooling times of 5-9 s, in conflict with the late-event bunches in kam-ii and bust after 8-9 s, which are also difficult to explain by background. speculative interpretations include the onset of fallback of transiently ejected material onto the ns, a late phase transition in the nuclear medium, e.g., from hadronic to quark matter, or other effects that add to the standard pns cooling emission and either stretch the signal or provide a late source of energy. more research, including systematic 3d simulations, is needed to assess these open issues. | supernova simulations confront sn 1987a neutrinos |
we examine the redshifts of a comprehensive set of published type ia supernovae, and provide a combined, improved catalogue with updated redshifts. we improve on the original catalogues by using the most up-to-date heliocentric redshift data available; ensuring all redshifts have uncertainty estimates; using the exact formulae to convert heliocentric redshifts into the cosmic microwave background (cmb) frame; and utilising an improved peculiar velocity model that calculates local motions in redshift-space and more realistically accounts for the external bulk flow at high-redshifts. we review 2607 supernova redshifts; 2285 are from unique supernovae and 322 are from repeat-observations of the same supernova. in total, we updated 990 unique heliocentric redshifts, and found 5 cases of missing or incorrect heliocentric corrections, 44 incorrect or missing supernova coordinates, 230 missing heliocentric or cmb frame redshifts, and 1200 missing redshift uncertainties. the absolute corrections range between $10^{-8} ≤ δ z ≤ 0.038$ , and rms $(δ z) ∼ 3{× 10^{-3}}$ . the sign of the correction was essentially random, so the mean and median corrections are small: $4{× 10^{-4}}$ and $4{× 10^{-6}}$ respectively. we examine the impact of these improvements for $h_0$ and the dark energy equation of state w and find that the cosmological results change by $δ h_0 = -0.12 km s^{-1}mpc^{-1}$ and $δ w = 0.003$ , both significantly smaller than previously reported uncertainties for $h_0$ of 1.0 $km s^{-1}mpc^{-1}$ and w of 0.04 respectively. | the pantheon+ analysis: improving the redshifts and peculiar velocities of type ia supernovae used in cosmological analyses |
despite the theoretical indication that fast neutrino-flavor conversion (ffc) ubiquitously occurs iin core-collapse supernovae and binary neutron star mergers, the lack of global simulations has been the greatest obstacle to study their astrophysical consequences. in this letter, we present large-scale (50 km) simulations of ffc in spherical symmetry by using a novel approach. we effectively rescale the oscillation scale of ffc by reducing the number of injected neutrinos in the simulation box, and then extrapolate back to the case of the target density of neutrinos with a convergence study. we find that ffc in all models achieves a quasisteady state in the nonlinear regime, and its saturation property of ffc is universal. we also find that temporal- and spatial variations of ffc are smeared out at large radii due to phase cancellation through neutrino self-interactions. finally, we provide a new diagnostic quantity, electron neutrino lepton number subtracted by heavy one angular crossing, to assess the nonlinear saturation of ffc. | time-dependent and quasisteady features of fast neutrino-flavor conversion |
identifying the astrophysical sites of the $r$-process, one of the primary mechanisms by which heavy elements are formed, is a key goal of modern astrophysics. the discovery of the brightest gamma-ray burst of all time, grb 221009a, at a relatively nearby redshift, presented the first opportunity to spectroscopically test the idea that $r$-process elements are produced following the collapse of rapidly rotating massive stars. here we present spectroscopic and photometric $\textit{james webb space telescope}$ (jwst) observations of grb 221009a obtained $+168$ and $+170$ rest-frame days after the initial gamma-ray trigger, and demonstrate they are well-described by a supernova (sn) and power-law afterglow, with no evidence for an additional component from $r$-process emission, and that the sn component strongly resembles the near-infrared spectra of previous sne, including sn 1998bw. we further find that the sn associated with grb 221009a is slightly fainter than the expected brightness of sn 1998bw at this phase, concluding that the sn is therefore not an unusual grb-sn. we infer a nickel mass of $\approx0.09$ m$_{\odot}$, consistent with the lack of an obvious sn detection in the early-time data. we find that the host galaxy of grb 221009a has a very low metallicity of $\approx0.12$ z$_{\odot}$ and our resolved host spectrum shows that grb 221009a occurred in a unique environment in its host characterized by strong h$_2$ emission lines consistent with recent star formation, which may hint at environmental factors being responsible for its extreme energetics. | jwst observations of the extraordinary grb 221009a reveal an ordinary supernova without signs of $r$-process enrichment in a low-metallicity galaxy |
the rate of supernovae in our local galactic neighbourhood within a distance of about 100 parsecs from earth is estimated to be one every 2-4 million years, based on the total rate in the milky way (2.0 ± 0.7 per century). recent massive-star and supernova activity in earth’s vicinity may be traced by radionuclides with half-lives of up to 100 million years, if trapped in interstellar dust grains that penetrate the solar system. one such radionuclide is 60fe (with a half-life of 2.6 million years), which is ejected in supernova explosions and winds from massive stars. here we report that the 60fe signal observed previously in deep-sea crusts is global, extended in time and of interstellar origin from multiple events. we analysed deep-sea archives from all major oceans for 60fe deposition via the accretion of interstellar dust particles. our results reveal 60fe interstellar influxes onto earth at 1.5-3.2 million years ago and at 6.5-8.7 million years ago. the signal measured implies that a few per cent of fresh 60fe was captured in dust and deposited on earth. our findings indicate multiple supernova and massive-star events during the last ten million years at distances of up to 100 parsecs. | recent near-earth supernovae probed by global deposition of interstellar radioactive 60fe |
here we analyse a particular type of f( r) gravity, the so-called exponential gravity which includes an exponential function of the ricci scalar in the action. such a term represents a correction to the usual hilbert-einstein action. by using supernovae ia, barionic acoustic oscillations, cosmic microwave background and h( z) data, the free parameters of the model are well constrained. the results show that such corrections to general relativity become important at cosmological scales and at late times, providing an alternative to the dark energy problem. in addition, the fits do not determine any significant difference statistically with respect to the λ cdm model. finally, such model is extended to include the inflationary epoch in the same gravitational lagrangian. as shown in the paper, the additional terms can reproduce the inflationary epoch and satisfy the constraints from planck data. | is exponential gravity a viable description for the whole cosmological history? |
we explore the final fates of massive intermediate-mass stars by computing detailed stellar models from the zero-age main sequence until near the end of the thermally pulsing phase. these super-asymptotic giant branch (super-agb) and massive agb star models are in the mass range between 5.0 and 10.0 m⊙ for metallicities spanning the range z = 0.02-0.0001. we probe the mass limits mup, mn and mmass, the minimum masses for the onset of carbon burning, the formation of a neutron star and the iron core-collapse supernovae, respectively, to constrain the white dwarf/electron-capture supernova (ec-sn) boundary. we provide a theoretical initial-to-final mass relation for the massive and ultra-massive white dwarfs and specify the mass range for the occurrence of hybrid co(ne) white dwarfs. we predict ec-sn rates for lower metallicities which are significantly lower than existing values from parametric studies in the literature. we conclude that the ec-sn channel (for single stars and with the critical assumption being the choice of mass-loss rate) is very narrow in initial mass, at most ≈0.2 m⊙. this implies that between ∼2 and 5 per cent of all gravitational collapse supernova are ec-sne in the metallicity range z = 0.02-0.0001. with our choice for mass-loss prescription and computed core growth rates, we find, within our metallicity range, that co cores cannot grow sufficiently massive to undergo a type 1.5 sn explosion. | super- and massive agb stars - iv. final fates - initial-to-final mass relation |
the dense neutrino medium in a core-collapse supernova or a neutron-star merger event can experience fast flavor conversions on time/distance scales that are much smaller than those of vacuum oscillations. it is believed that fast neutrino flavor transformation occurs in the region where the angular distributions of νe and ν¯e cross each other. we present the first study of this crossing phenomenon and the fast neutrino flavor conversions in multidimensional (multi-d) supernova models. we examine the neutrino distributions obtained by solving the boltzmann transport equation for several fixed profiles which are representative snapshots taken from separate 2d and 3d supernova simulations with an 11.2 m⊙ progenitor model. our research shows that the spherically asymmetric patterns of the νe and ν¯e fluxes in multi-d models can assist the appearance of the crossing between the νe and ν¯e angular distributions. in the models that we have studied, there exist unstable neutrino oscillation modes in and beyond the neutrino decoupling region which have amplitude growth rates as large as an e -fold per nanosecond. this finding can have important consequences for the explosion mechanism, nucleosynthesis, and neutrino signals of core-collapse supernovae. | on the occurrence of fast neutrino flavor conversions in multidimensional supernova models |
the heliocentric redshifts (zhel) reported for 150 type ia supernovae in the pantheon compilation are significantly discrepant from their corresponding values in the jla compilation. both catalogues include corrections to the redshifts and magnitudes of the supernovae to account for the motion of the heliocentric frame relative to the 'cmb rest frame', as well as corrections for the directionally coherent bulk motion of local galaxies with respect to this frame. the latter is done employing modelling of peculiar velocities which assume the λcdm cosmological model but nevertheless provide evidence for residual bulk flows which are discordant with this model (implying that the observed universe is in fact anisotropic). until recently such peculiar velocity corrections in the pantheon catalogue were made at redshifts exceeding 0.2 although there is no data on which to base such corrections. we study the impact of these vexed issues on the 4.4σ discrepancy between the hubble constant of h0 = 67.4 ± 0.5 km s-1 mpc-1 inferred from observations of cmb anisotropies by planck assuming λcdm, and the measurement of h0 = 73.5 ± 1.4 km s-1 mpc-1 by the sh0es project which extended the local distance ladder using type ia supernovae. using the same methodology as the latter study we find that for supernovae whose redshifts are discrepant between pantheon and jla with δzhel > 0.0025, the pantheon redshifts favour h0 ≃ 72 km s-1 mpc-1, while the jla redshifts favour h0 ≃ 68 km s-1 mpc-1. thus the discrepancies between sne ia datasets are sufficient to undermine the claimed 'hubble tension'. we further note the systematic variation of h0 by ~6-9 km s-1 mpc-1 across the sky seen in multiple datasets, implying that it cannot be measured locally to better than ~10% in a model-independent manner. | is there really a hubble tension? |
based on recent results from three-dimensional supernova simulations and semi-analytical parametrized models, we develop analytical prescriptions for the dependence of the mass of neutron stars and black holes and the natal kicks, if any, on the pre-supernova carbon-oxygen core and helium shell masses. our recipes are probabilistic rather than deterministic in order to account for the intrinsic stochasticity of stellar evolution and supernovae. we anticipate that these recipes will be particularly useful for rapid population synthesis, and we illustrate their application to distributions of remnant masses and kicks for a population of single stars. | simple recipes for compact remnant masses and natal kicks |
recent versions of the observed cosmic star formation history (sfh) have resolved an inconsistency with the stellar mass density history. we show that the revised sfh also scales up the delay-time distribution (dtd) of type ia supernovae (sne ia), as determined from the observed volumetric sn ia rate history, aligning it with other field-galaxy sn ia dtd measurements. the revised-sfh-based dtd has a {t}-1.1+/- 0.1 form and a hubble-time-integrated production efficiency of n/{m}\star =1.3+/- 0.1 sne ia per 1000 {m}⊙of formed stellar mass. using these revised histories and updated empirical iron yields of the various sn types, we re-derive the cosmic iron accumulation history. core-collapse sne and sne ia have contributed about equally to the total mass of iron in the universe today. we find the track of the average cosmic gas element in the [α/fe] versus [fe/h] abundance-ratio plane. the track is broadly similar to the observed main locus of galactic stars in this plane, indicating a milky way (mw) sfh similar in form to the cosmic one. we easily find a simple mw sfh that makes the track closely match this stellar locus. galaxy clusters appear to have a higher-normalization dtd. this cluster dtd, combined with a short-burst mw sfh peaked at z = 3, produces a track that matches remarkably well the observed “high-α” locus of mw stars, suggesting the halo/thick-disk population has had a galaxy-cluster-like formation mode. thus, a simple two-component sfh, combined with empirical dtds and sn iron yields, suffices to closely reproduce the mw’s stellar abundance patterns. | star formation, supernovae, iron, and α: consistent cosmic and galactic histories |
flavor-dependent neutrino emission is critical to the evolution of a supernova and its neutrino signal. in the dense anisotropic interior of the star, neutrino-neutrino forward scattering can lead to fast collective neutrino oscillations, which has striking consequences. we present a theory of fast flavor depolarization, explaining how neutrino flavor differences become smaller, i.e., depolarize, due to diffusion to smaller angular scales. we show that transverse relaxation determines the epoch of this irreversible depolarization. we give a method to compute the depolarized fluxes, presenting an explicit formula for simple initial conditions, which can be a crucial input for supernova theory and neutrino phenomenology. | fast flavor depolarization of supernova neutrinos |
we present hubble space telescope imaging of a pre-explosion counterpart to sn 2019yvr obtained 2.6 yr before its explosion as a type ib supernova (sn ib). aligning to a post-explosion gemini-s/gsaoi image, we demonstrate that there is a single source consistent with being the sn 2019yvr progenitor system, the second sn ib progenitor candidate after iptf13bvn. we also analysed pre-explosion spitzer/infrared array camera (irac) imaging, but we do not detect any counterparts at the sn location. sn 2019yvr was highly reddened, and comparing its spectra and photometry to those of other, less extinguished sne ib we derive $e(b-v)=0.51\substack{+0.27\\ -0.16}$ mag for sn 2019yvr. correcting photometry of the pre-explosion source for dust reddening, we determine that this source is consistent with a log (l/l⊙) = 5.3 ± 0.2 and $t_{\mathrm{eff}} = 6800\substack{+400\\ -200}$ k star. this relatively cool photospheric temperature implies a radius of 320$\substack{+30\\ -50}~\mathrm{ r}_{\odot}$, much larger than expectations for sn ib progenitor stars with trace amounts of hydrogen but in agreement with previously identified sn iib progenitor systems. the photometry of the system is also consistent with binary star models that undergo common envelope evolution, leading to a primary star hydrogen envelope mass that is mostly depleted but still seemingly in conflict with the sn ib classification of sn 2019yvr. sn 2019yvr had signatures of strong circumstellar interaction in late-time (>150 d) spectra and imaging, and so we consider eruptive mass-loss and common envelope evolution scenarios that explain the sn ib spectroscopic class, pre-explosion counterpart, and dense circumstellar material. we also hypothesize that the apparent inflation could be caused by a quasi-photosphere formed in an extended, low-density envelope, or circumstellar matter around the primary star. | a cool and inflated progenitor candidate for the type ib supernova 2019yvr at 2.6 yr before explosion |
we report alma band 9 continuum observations of the normal, dusty star-forming galaxy a1689-zd1 at z = 7.13, resulting in a ~4.6 σ detection at 702 ghz. for the first time, these observations probe the far-infrared spectrum shortward of the emission peak of a galaxy in the epoch of reionization (eor). together with ancillary data from earlier works, we derive the dust temperature, td, and mass, md, of a1689-zd1 using both traditional modified blackbody spectral energy density fitting, and a new method that relies only on the [c ii] 158 μm line and underlying continuum data. the two methods give $t_{\rm d} = (42^{+13}_{-7}, 40^{+13}_{-7}$) k, and $m_{\rm d} = (1.7^{+1.3}_{-0.7}, 2.0^{+1.8}_{-1.0})\, \times {}\, 10^{7} \, \mathrm{ m}_{\odot }$. band 9 observations improve the accuracy of the dust temperature (mass) estimate by ~50 per cent (6 times). the derived temperatures confirm the reported increasing td-redshift trend between z = 0 and 8; the dust mass is consistent with a supernova origin. although a1689-zd1 is a normal uv-selected galaxy, our results, implying that ~85 per cent of its star-formation rate is obscured, underline the non-negligible effects of dust in eor galaxies. | accurate dust temperature determination in a z = 7.13 galaxy |
relativistic magnetohydrodynamics (rmhd) provides an extremely useful description of the low-energy long-wavelength phenomena in a variety of physical systems from quark–gluon plasma in heavy-ion collisions to matters in supernova, compact stars, and early universe. we review the recent theoretical progresses of rmhd, such as a formulation of rmhd from the perspective of magnetic flux conservation using the entropy–current analysis, the nonequilibrium statistical operator approach applied to quantum electrodynamics, and the relativistic kinetic theory. we discuss how the transport coefficients in rmhd are computed in kinetic theory and perturbative quantum field theories. we also explore the collective modes and instabilities in rmhd with a special emphasis on the role of chirality in a parity-odd plasma. we also give some future prospects of rmhd, including the interaction with spin hydrodynamics and the new kinetic framework with magnetic flux conservation. | new developments in relativistic magnetohydrodynamics |
the soft x-ray focusing telescope (sxt), india's first x-ray telescope based on the principle of grazing incidence, was launched aboard the astrosat and made operational on october 26, 2015. x-rays in the energy band of 0.3-8.0 kev are focussed on to a cooled charge coupled device thus providing medium resolution x-ray spectroscopy of cosmic x-ray sources of various types. it is the most sensitive x-ray instrument aboard the astrosat. in its first year of operation, sxt has been used to observe objects ranging from active stars, compact binaries, supernova remnants, active galactic nuclei and clusters of galaxies in order to study its performance and quantify its characteriztics. here, we present an overview of its design, mechanical hardware, electronics, data modes, observational constraints, pipeline processing and its in-orbit performance based on preliminary results from its characterization during the performance verification phase. | soft x-ray focusing telescope aboard astrosat: design, characteristics and performance |
next-generation surveys like the legacy survey of space and time (lsst) on the vera c. rubin observatory will generate orders of magnitude more discoveries of transients and variable stars than previous surveys. to prepare for this data deluge, we developed the photometric lsst astronomical time-series classification challenge (plasticc), a competition which aimed to catalyze the development of robust classifiers under lsst-like conditions of a non-representative training set for a large photometric test set of imbalanced classes. over 1,000 teams participated in plasticc, which was hosted in the kaggle data science competition platform between sep 28, 2018 and dec 17, 2018, ultimately identifying three winners in february 2019. participants produced classifiers employing a diverse set of machine learning techniques including hybrid combinations and ensemble averages of a range of approaches, among them boosted decision trees, neural networks, and multi-layer perceptrons. the strong performance of the top three classifiers on type ia supernovae and kilonovae represent a major improvement over the current state-of-the-art within astronomy. this paper summarizes the most promising methods and evaluates their results in detail, highlighting future directions both for classifier development and simulation needs for a next generation plasticc data set. | results of the photometric lsst astronomical time-series classification challenge (plasticc) |
peculiar velocity measurements are the only tool available in the low-redshift universe for mapping the large-scale distribution of matter and can thus be used to constrain cosmology. using redshifts from the 2m++ redshift compilation, we reconstruct the density of galaxies within 200 h-1 mpc, allowing for the first time good sampling of important superclusters such as the shapley concentration. we compare the predicted peculiar velocities from 2m++ to tully-fisher and sne peculiar velocities. we find a value of β* ≡ ω m^{0.55}/b^* = 0.431 ± 0.021, suggesting ω m^{0.55}σ _{8,lin} = 0.401 ± 0.024, in good agreement with other probes. the predicted peculiar velocity of the local group arising from the 2m++ volume alone is 540 ± 40 km s-1, towards l = 268° ± 4°, b = 38° ± 6°, only 10° out of alignment with the cosmic microwave background dipole. to account for velocity contributions arising from sources outside the 2m++ volume, we fit simultaneously for β* and an external bulk flow in our analysis. we find that an external bulk flow is preferred at the 5.1σ level, and the best fit has a velocity of 159 ± 23 km s- 1 towards l = 304° ± 11°, b = 6° ± 13°. finally, the predicted bulk flow of a 50 h-1 mpc gaussian-weighted volume centred on the local group is 230 ± 30 km s-1, in the direction l = 293° ± 8°, b = 14° ± 10°, in agreement with predictions from λ cold dark matter. | cosmological parameters from the comparison of peculiar velocities with predictions from the 2m++ density field |
we perform a systematic study of merging black hole (bh) binaries with compact star (cs) companions, including black hole-white dwarf (bh-wd), black hole-neutron star (bh-ns), and black hole-black hole (bh-bh) systems. previous studies have shown that mass transfer stability and common envelope evolution can significantly affect the formation of merging bh-cs binaries through isolated binary evolution. with detailed binary evolution simulations, we obtain easy-to-use criteria for the occurrence of the common envelope phase in mass-transferring bh binaries with a nondegenerate donor, and incorporate the criteria into population synthesis calculations. to explore the impact of a possible mass gap between nss and bhs on the properties of merging bh-cs binary population, we adopt different supernova mechanisms involving the rapid, delayed, and stochastic prescriptions to deal with the compact remnant masses and the natal kicks. our calculations show that there are ~105-106 bh-cs binaries in the milky way, among which dozens are observable by future space-based gravitational wave detectors. we estimate that the local merger rate density of all bh-cs systems is ~60-200 gpc-3 yr-1. while there are no low-mass bhs formed via rapid supernovae, both delayed and stochastic prescriptions predict that ~100%/~70%/~30% of merging bh-wd/bh-ns/bh-bh binaries are likely to have bh components within the mass gap. | population synthesis of black hole binaries with compact star companions |
we apply the effective field theory of large-scale structure (eftoflss) to analyze cosmological models with clustering quintessence, which allows us to consistently describe the parameter region in which the quintessence equation of state $w < - 1$. first, we extend the description of biased tracers in redshift space to the presence of clustering quintessence, and compute the one-loop power spectrum. we solve the eftoflss equations using the exact time dependence, which is relevant to obtain unbiased constraints. then, fitting the full shape of boss pre-reconstructed power spectrum measurements, the boss post-reconstruction bao measurements, bao measurements from 6df/mgs and eboss, the supernovae from pantheon, and a prior from bbn, we bound the clustering quintessence equation of state parameter $w=-1.011_{-0.048}^{+0.053}$ at $68\%$ c.l.. further combining with planck, we obtain $w=-1.028_{-0.030}^{+0.037}$ at $68\%$ c.l.. we also obtain constraints on smooth quintessence, in the physical regime $w \geq -1$: combining all datasets, we get $-1\leq w < - 0.979$ at $68\%$ c.l.. these results strongly support a cosmological constant. | limits on clustering and smooth quintessence from the eftoflss |
we present james webb space telescope (jwst) and hubble space telescope (hst) observations of the afterglow of grb 221009a, the brightest gamma-ray burst (grb) ever observed. this includes the first mid-ir spectra of any grb, obtained with jwst/near infrared spectrograph (0.6-5.5 micron) and mid-infrared instrument (5-12 micron), 12 days after the burst. assuming that the intrinsic spectral slope is a single power law, with fν∝ ν -β , we obtain β ≈ 0.35, modified by substantial dust extinction with av= 4.9. this suggests extinction above the notional galactic value, possibly due to patchy extinction within the milky way or dust in the grb host galaxy. it further implies that the x-ray and optical/ir regimes are not on the same segment of the synchrotron spectrum of the afterglow. if the cooling break lies between the x-ray and optical/ir, then the temporal decay rates would only match a post-jet-break model, with electron index p < 2, and with the jet expanding into a uniform ism medium. the shape of the jwst spectrum is near-identical in the optical/near-ir to x-shooter spectroscopy obtained at 0.5 days and to later time observations with hst. the lack of spectral evolution suggests that any accompanying supernova (sn) is either substantially fainter or bluer than sn 1998bw, the proto-type grb-sn. our hst observations also reveal a disk-like host galaxy, viewed close to edge-on, that further complicates the isolation of any sn component. the host galaxy appears rather typical among long-grb hosts and suggests that the extreme properties of grb 221009a are not directly tied to its galaxy-scale environment. | the first jwst spectrum of a grb afterglow: no bright supernova in observations of the brightest grb of all time, grb 221009a |
while conventional type ia supernova (sn ia) cosmology analyses rely primarily on rest-frame optical light curves to determine distances, sne ia are excellent standard candles in near-infrared (nir) light, which is significantly less sensitive to dust extinction. an sn ia spectral energy distribution (sed) model capable of fitting rest-frame nir observations is necessary to fully leverage current and future sn ia data sets from ground- and space-based telescopes including hst, lsst, jwst, and rst. we construct a hierarchical bayesian model for sn ia seds, continuous over time and wavelength, from the optical to nir (b through h, or $0.35{-}1.8\, \mu$m). we model the sed as a combination of physically distinct host galaxy dust and intrinsic spectral components. the distribution of intrinsic seds over time and wavelength is modelled with probabilistic functional principal components and the covariance of residual functions. we train the model on a nearby sample of 79 sne ia with joint optical and nir light curves by sampling the global posterior distribution over dust and intrinsic latent variables, sed components and population hyperparameters. photometric distances of sne ia with nir data near maximum obtain a total rms error of 0.10 mag with our bayesn model, compared to 0.13-0.14 mag with salt2 and snoopy for the same sample. jointly fitting the optical and nir data of the full sample up to moderate reddening (host e(b - v) < 0.4) for a global host dust law, we find rv = 2.9 ± 0.2, consistent with the milky way average. | a hierarchical bayesian sed model for type ia supernovae in the optical to near-infrared |
we calculate the gravitational-wave (gw) signatures of detailed three-dimensional (3d) core-collapse supernova simulations spanning a range of massive stars. most of the simulations are carried out to times late enough to capture more than 95% of the total gw emission. we find that the f /g -mode and f -mode of protoneutron star oscillations carry away most of the gw power. the f -mode frequency inexorably rises as the protoneutron star (pns) core shrinks. we demonstrate that the gw emission is excited mostly by accretion plumes onto the pns that energize modal oscillations and also high-frequency ("haze") emission correlated with the phase of violent accretion. the duration of the major phase of emission varies with exploding progenitor, and there is a strong correlation between the total gw energy radiated and the compactness of the progenitor. moreover, the total gw emissions vary by as much as 3 orders of magnitude from star to star. for black hole formation, the gw signal tapers off slowly and does not manifest the haze seen for the exploding models. for such failed models, we also witness the emergence of a spiral shock motion that modulates the gw emission at a frequency near ∼100 hz that slowly increases as the stalled shock sinks. we find significant angular anisotropy of both the high- and low-frequency (memory) gw emissions, though the latter have very little power. | gravitational-wave signature of core-collapse supernovae |
we explore with self-consistent 2d f ornax simulations the dependence of the outcome of collapse on many-body corrections to neutrino-nucleon cross sections, the nucleon-nucleon bremsstrahlung rate, electron capture on heavy nuclei, pre-collapse seed perturbations, and inelastic neutrino-electron and neutrino-nucleon scattering. importantly, proximity to criticality amplifies the role of even small changes in the neutrino-matter couplings, and such changes can together add to produce outsized effects. when close to the critical condition the cumulative result of a few small effects (including seeds) that individually have only modest consequence can convert an anemic into a robust explosion, or even a dud into a blast. such sensitivity is not seen in one dimension and may explain the apparent heterogeneity in the outcomes of detailed simulations performed internationally. a natural conclusion is that the different groups collectively are closer to a realistic understanding of the mechanism of core-collapse supernovae than might have seemed apparent. | crucial physical dependencies of the core-collapse supernova mechanism |
massive stars are important metal factories in the universe. they have short and energetic lives, and many of them inevitably explode as a supernova and become a neutron star or black hole. in turn, the formation, evolution and explosive deaths of massive stars impact the surrounding interstellar medium and shape the evolution of their host galaxies. yet the chemical and dynamical evolution of a massive star, including the chemical yield of the ultimate supernova and the remnant mass of the compact object, strongly depend on the interior physics of the progenitor star. we currently lack empirically calibrated prescriptions for various physical processes at work within massive stars, but this is now being remedied by asteroseismology. the study of stellar structure and evolution using stellar oscillations -- asteroseismology -- has undergone a revolution in the last two decades thanks to high-precision time series photometry from space telescopes. in particular, the long-term light curves provided by the most, corot, brite, kepler/k2 and tess missions provided invaluable data sets in terms of photometric precision, duration and frequency resolution to successfully apply asteroseismology to massive stars and probe their interior physics. the observation and subsequent modelling of stellar pulsations in massive stars has revealed key missing ingredients in stellar structure and evolution models of these stars. thus asteroseismology has opened a new window into calibrating stellar physics within a highly degenerate part of the hertzsprung--russell diagram. in this review, i provide a historical overview of the progress made using ground-based and early space missions, and discuss more recent advances and breakthroughs in our understanding of massive star interiors by means of asteroseismology with modern space telescopes. | asteroseismology of high-mass stars: new insights of stellar interiors with space telescopes |
automated photometric supernova classification has become an active area of research in recent years in light of current and upcoming imaging surveys such as the dark energy survey (des) and the large synoptic survey telescope, given that spectroscopic confirmation of type for all supernovae discovered will be impossible. here, we develop a multi-faceted classification pipeline, combining existing and new approaches. our pipeline consists of two stages: extracting descriptive features from the light curves and classification using a machine learning algorithm. our feature extraction methods vary from model-dependent techniques, namely salt2 fits, to more independent techniques that fit parametric models to curves, to a completely model-independent wavelet approach. we cover a range of representative machine learning algorithms, including naive bayes, k-nearest neighbors, support vector machines, artificial neural networks, and boosted decision trees (bdts). we test the pipeline on simulated multi-band des light curves from the supernova photometric classification challenge. using the commonly used area under the curve (auc) of the receiver operating characteristic as a metric, we find that the salt2 fits and the wavelet approach, with the bdts algorithm, each achieve an auc of 0.98, where 1 represents perfect classification. we find that a representative training set is essential for good classification, whatever the feature set or algorithm, with implications for spectroscopic follow-up. importantly, we find that by using either the salt2 or the wavelet feature sets with a bdt algorithm, accurate classification is possible purely from light curve data, without the need for any redshift information. | photometric supernova classification with machine learning |
we present the discovery that asassn-14ko is a periodically flaring active galactic nucleus at the center of the galaxy eso 253-g003. at the time of its discovery by the all-sky automated survey for supernovae (asas-sn), it was classified as a supernova close to the nucleus. the subsequent 6 yr of v- and g-band asas-sn observations revealed that asassn-14ko has nuclear flares occurring at regular intervals. the 17 observed outbursts show evidence of a decreasing period over time, with a mean period of p0 = 114.2 ± 0.4 days and a period derivative of $\dot{p}=-0.0017\pm 0.0003$ <!-- --> . the most recent outburst in 2020 may, which took place as predicted, exhibited spectroscopic changes during the rise and had a uv bright, blackbody spectral energy distribution similar to tidal disruption events (tdes). the x-ray flux decreased by a factor of 4 at the beginning of the outburst and then returned to its quiescent flux after ∼8 days. the transiting exoplanet survey satellite observed an outburst during sectors 4-6, revealing a rise time of 5.60 ± 0.05 days in the optical and a decline that is best fit with an exponential model. we discuss several possible scenarios to explain asassn-14ko's periodic outbursts, but currently favor a repeated partial tde. the next outbursts should peak in the optical on ut 2020 september 7.4±1.1 and ut 2020 december 26.5±1.4. | asassn-14ko is a periodic nuclear transient in eso 253-g003 |
observations of x-ray binaries indicate a dearth of compact objects in the mass range from ∼2 − 5 m⊙. the existence of this (first mass) gap has been used to discriminate between proposed engines behind core-collapse supernovae. from ligo/virgo observations of binary compact remnant masses, several candidate first mass gap objects, either neutron stars (nss) or black holes (bhs), were identified during the o3 science run. motivated by these new observations, we study the formation of bh-ns mergers in the framework of isolated classical binary evolution, using population synthesis methods to evolve large populations of binary stars (population i and ii) across cosmic time. we present results on the ns to bh mass ratios (q = mns/mbh ) in merging systems, showing that although systems with a mass ratio as low as q = 0.02 can exist, typically bh-ns systems form with moderate mass ratios q = 0.1 − 0.2. if we adopt a delayed supernova engine, we conclude that ∼30% of bh-ns mergers may host at least one compact object in the first mass gap (fmg). even allowing for uncertainties in the processes behind compact object formation, we expect the fraction of bh-ns systems ejecting mass during the merger to be small (from ∼0.6 − 9%). in our reference model, we assume: (i) the formation of compact objects within the fmg, (ii) natal ns/bh kicks decreased by fallback, (iii) low bh spins due to tayler-spruit angular momentum transport in massive stars. we find that ≲1% of bh-ns mergers will have any mass ejection and about the same percentage will produce kilonova bright enough to have a chance of being detected with a large (subaru-class) 8 m telescope. interestingly, all these mergers will have both a bh and an ns in the fmg. | black hole-neutron star mergers: the first mass gap and kilonovae |
the kilonova (kn) associated with the binary neutron star (bns) merger gw170817 is the only known electromagnetic counterpart to a gravitational wave source. here we produce a sequence of radiative transfer models (using tardis) with updated atomic data, and compare them to accurately calibrated spectra. we use element compositions from nuclear network calculations based on a realistic hydrodynamical simulation of a bns merger. we show that the blue spectrum at +1.4 d after merger requires a nucleosynthetic trajectory with a high electron fraction. our best-fitting model is composed entirely of first r-process peak elements (sr and zr) and the strong absorption feature is reproduced well by sr ii absorption. at this epoch, we set an upper limit on the lanthanide mass fraction of $x_{{\small ln}} \lesssim 5 \times 10^{-3}$. in contrast, all subsequent spectra from +2.4 to 6.4 d require the presence of a modest amount of lanthanide material ($x_{{\small ln}} \simeq 0.05^{+0.05}_{-0.02}$), produced by a trajectory with ye = 0.29. this produces lanthanide-induced line blanketing below 6000 å, and sufficient light r-process elements to explain the persistent strong feature at ~0.7-1.0 $\mu$m (sr ii). the composition gives good matches to the observed data, indicating that the strong blue flux deficit results in the near-infrared (nir) excess. the disjoint in composition between the first epoch and all others indicates either ejecta stratification, or the presence of two distinct components of material. this further supports the 'two-component' kn model, and constrains the element composition from nucleosynthetic trajectories. the major uncertainties lie in availability of atomic data and the ionization state of the expanding material. | modelling the spectra of the kilonova at2017gfo - i. the photospheric epochs |
natal kicks and spins are characteristic properties of neutron stars (nss) and black holes (bhs). both offer valuable clues to dynamical processes during stellar core collapse and explosion. moreover, they influence the evolution of stellar multiple systems and the gravitational-wave signals from their inspiral and merger. observational evidence of a possibly generic spin-kick alignment has been interpreted as an indication that ns spins are either induced with the ns kicks or inherited from the progenitor rotation, which thus might play a dynamically important role during stellar collapse. current three-dimensional supernova simulations suggest that ns kicks are transferred in the first seconds of the explosion, mainly by anisotropic mass ejection and, on a secondary level, anisotropic neutrino emission. by contrast, the ns spins are only determined minutes to hours later by the angular momentum associated with the fallback of matter that does not become gravitationally unbound in the supernova. here, we propose a novel scenario to explain spin-kick alignment as a consequence of tangential vortex flows in the fallback matter that is accreted mostly from the direction of the ns's motion. for this effect the initial ns kick is crucial, because it produces a growing offset of the ns away from the explosion center, thus promoting one-sided accretion. in this new scenario conclusions based on traditional concepts are reversed. for example, pre-kick ns spins are not required, and rapid progenitor core rotation can hamper spin-kick alignment. we also discuss implications for natal bh kicks and the possibility of tossing the bh's spin axis during its formation. | supernova fallback as origin of neutron star spins and spin-kick alignment |
we present 3d simulations of the core-collapse of massive rotating and non-rotating progenitors performed with the general relativistic neutrino hydrodynamics code coconut-fmt. the progenitor models include wolf-rayet stars with initial helium star masses of $39\, \mathrm{ m}_{\odot }$ and $20\, \mathrm{ m}_{\odot }$ , and an $18\, \mathrm{ m}_{\odot }$ red supergiant. the $39\, \mathrm{ m}_{\odot }$ model is a rapid rotator, whereas the two other progenitors are non-rotating. both wolf-rayet models produce healthy neutrino-driven explosions, whereas the red supergiant model fails to explode. by the end of the simulations, the explosion energies have already reached $1.1\times 10^{51}\, $ and $0.6\times 10^{51}\, \mathrm{erg}$ for the $39\, \mathrm{ m}_{\odot }$ and $20\, \mathrm{ m}_{\odot }$ model, respectively. they produce neutron stars of relatively high mass, but with modest kicks. due to the alignment of the bipolar explosion geometry with the rotation axis, there is a relatively small misalignment of 30° between the spin and the kick in the rapidly rotating $39\, \mathrm{ m}_{\odot }$ model. for this model, we find that rotation significantly changes the dependence of the characteristic gravitational-wave frequency of the f-mode on the proto-neutron star parameters compared to the non-rotating case. its gravitational-wave amplitudes would make it detectable out to almost 2 mpc by the einstein telescope. the other two progenitors have considerably smaller detection distances, despite significant low-frequency emission in the most sensitive frequency band of current gravitational-wave detectors. | three-dimensional core-collapse supernova simulations of massive and rotating progenitors |
the swift-detected grb 060614 was a unique burst that straddles an imaginary divide between long- and short-duration gamma-ray bursts (grbs), and its physical origin has been heavily debated over the years. recently, a distinct, very soft f814w-band excess at t∼ 13.6 days after the burst was identified in a joint-analysis of vlt and hubble space telescope optical afterglow data of grb 060614, which has been interpreted as evidence for an accompanying macronova (also called a kilonova). under the assumption that the afterglow data in the time interval of 1.7-3.0 days after the burst are due to external fs emission, when this assumption is extrapolated to later times it is found that there is an excess of flux in several multi-band photometric observations. this component emerges at ∼4 days after the burst, and it may represent the first time that a multi-epoch/band light curve of a macronova has been obtained. the macronova associated with grb 060614 peaked at t≲ 4 days after the burst, which is significantly earlier than that observed for a supernova associated with a long-duration grb. due to the limited data, no strong evidence for a temperature evolution is found. we derive a conservative estimate of the macronova rate of ∼ {16.3}-8.2+16.3 {{gpc}}-3 {{yr}}-1, implying a promising prospect for detecting the gravitational wave radiation from compact-object mergers by upcoming advanced ligo/virgo/kagra detectors (i.e., the rate is {{r}}{gw}∼ {0.5}-0.25+0.5{(d/200 {mpc})}3 {{yr}}-1). | the light curve of the macronova associated with the long-short burst grb 060614 |
superluminous supernovae (slsne) are very bright explosions that were only discovered recently and that show a preference for occurring in faint dwarf galaxies. understanding why stellar evolution yields different types of stellar explosions in these environments is fundamental in order to both uncover the elusive progenitors of slsne and to study star formation in dwarf galaxies. in this paper, we present the first results of our project to study superluminous supernova host galaxies, focusing on the sample for which we have obtained spectroscopy. we show that slsne-i and slsne-r (hydrogen-poor) often (∼50 per cent in our sample) occur in a class of galaxies that is known as extreme emission line galaxies (eelgs). the probability of this happening by chance is negligible and we therefore conclude that the extreme environmental conditions and the slsn phenomenon are related. in contrast, slsne-ii (hydrogen-rich) occur in more massive, more metal-rich galaxies with softer radiation fields. therefore, if slsne-ii constitute a uniform class, their progenitor systems are likely different from those of h-poor slsne. gamma-ray bursts (grbs) are, on average, not found in as extreme environments as h-poor slsne. we propose that h-poor slsne result from the very first stars exploding in a starburst, even earlier than grbs. this might indicate a bottom-light initial mass function in these systems. slsne present a novel method of selecting candidate eelgs independent of their luminosity. | spectroscopy of superluminous supernova host galaxies. a preference of hydrogen-poor events for extreme emission line galaxies |
we examine the claimed excess x-ray line emission near 3.5 kev including both a new analysis of xmm-newton observations of the milky way centre and a reanalysis of the data on m 31 and clusters. in no case do we find conclusive evidence for an excess. in the case of the galactic centre, we show that known plasma lines, including in particular k xviii lines at 3.48 and 3.52 kev, provide a satisfactory fit to the xmm data. we estimate the expected flux of the k xviii lines and find that the measured line flux falls squarely within the predicted range based on the brightness of other well-measured lines in the energy range of interest and on detailed multitemperature plasma models. we then re-assess the evidence for excess emission from clusters of galaxies, allowing for systematic uncertainty in the expected flux from known plasma lines and additional uncertainty due to potential variation in the abundances of different elements. we find that no conclusive excess line emission can be advocated when considering systematic uncertainties in perseus or in other clusters. we also reanalyse the xmm data for m 31 and find no statistically significant line emission near 3.5 kev to a level greater than 1σ. finally, we analyse the tycho supernova remnant, which shows similar plasma features to the sources above, but does not host any significant dark matter. we detect a 3.55 kev line from tycho, which points to possible systematic effects in the flux determination of weak lines, or to relative elemental abundances vastly different from theoretical expectations. | discovery of a 3.5 kev line in the galactic centre and a critical look at the origin of the line across astronomical targets |
we present gravitational wave (gw) signal predictions from four 3d multigroup neutrino hydrodynamics simulations of core-collapse supernovae of progenitors with 11.2, 20 and 27 m⊙. gw emission in the pre-explosion phase strongly depends on whether the post-shock flow is dominated by the standing accretion shock instability (sasi) or convection and differs considerably from 2d models. sasi activity produces a strong signal component below 250 hz through asymmetric mass motions in the gain layer and a non-resonant coupling to the proto-neutron star (pns). both convection- and sasi-dominated models show gw emission above 250 hz, but with considerably lower amplitudes than in 2d. this is due to a different excitation mechanism for high-frequency l = 2 motions in the pns surface, which are predominantly excited by pns convection in 3d. resonant excitation of high-frequency surface g modes in 3d by mass motions in the gain layer is suppressed compared to 2d because of smaller downflow velocities and a lack of high-frequency variability in the downflows. in the exploding 20 m⊙ model, shock revival results in enhanced low-frequency emission due to a change of the preferred scale of the convective eddies in the pns convection zone. estimates of the expected excess power in two frequency bands suggest that second-generation detectors will only be able to detect very nearby events, but that third-generation detectors could distinguish sasi- and convection-dominated models at distances of ∼ 10 kpc. | gravitational wave signals from 3d neutrino hydrodynamics simulations of core-collapse supernovae |
we performed a detailed analysis of the detectability of a wide range of gravitational waves derived from core-collapse supernova simulations using gravitational-wave detector noise scaled to the sensitivity of the upcoming fourth and fifth observing runs of the advanced ligo, advanced virgo, and kagra. we use the coherent waveburst algorithm, which was used in the previous observing runs to search for gravitational waves from core-collapse supernovae. as coherent waveburst makes minimal assumptions on the morphology of a gravitational-wave signal, it can play an important role in the first detection of gravitational waves from an event in the milky way. we predict that signals from neutrino-driven explosions could be detected up to an average distance of 10 kpc, and distances of over 100 kpc can be reached for explosions of rapidly-rotating progenitor stars. an estimated minimum signal-to-noise ratio of 10-25 is needed for the signals to be detected. we quantify the accuracy of the waveforms reconstructed with coherent waveburst and we determine that the most challenging signals to reconstruct are those produced in long-duration neutrino-driven explosions, and models that form black holes a few seconds after the core bounce. | detecting and reconstructing gravitational waves from the next galactic core-collapse supernova in the advanced detector era |
neutrino flavor instabilities have the potential to shuffle neutrinos between electron, mu, and tau flavor states, possibly modifying the core-collapse supernova mechanism and the heavy elements ejected from neutron star mergers. analytic methods indicate the presence of so-called fast flavor transformation instabilities, and numerical simulations can be used to probe the nonlinear evolution of the neutrinos. simulations of the fast flavor instability to date have been performed assuming imposed symmetries. we perform simulations of the fast flavor instability that include all three spatial dimensions and all relevant momentum dimensions in order to probe the validity of these approximations. if the fastest growing mode has a wave number along a direction of imposed symmetry, then the instability can be suppressed. the late-time equilibrium distribution of flavor, however, seems to be little affected by the number of spatial dimensions. this is a promising hint that the results of lower-dimensionality simulations to date have predictions that are robust against their the number of spatial dimensions, though simulations of a wider variety of neutrino distributions need to be carried out to support this claim more generally. | neutrino fast flavor instability in three dimensions |
we review the lives, deaths and nucleosynthetic signatures of intermediate-mass stars in the range ≈6-12 m⊙, which form super-agb stars near the end of their lives. the critical mass boundaries both between different types of massive white dwarfs (co, co-ne, one), and between white dwarfs and supernovae, are examined along with the relative fraction of super-agb stars that end life either as an one white dwarf or as a neutron star (or an onefe white dwarf), after undergoing an electron capture supernova event. the contribution of the other potential single-star channel to electron-capture supernovae, that of the failed massive stars, is also discussed. the factors that influence these different final fates and mass limits, such as composition, rotation, the efficiency of convection, the nuclear reaction rates, mass-loss rates, and third dredge-up efficiency, are described. we stress the importance of the binary evolution channels for producing electron-capture supernovae. recent nucleosynthesis calculations and elemental yield results are discussed and a new set of s-process heavy element yields is presented. the contribution of super-agb star nucleosynthesis is assessed within a galactic perspective, and the (super-)agb scenario is considered in the context of the multiple stellar populations seen in globular clusters. a brief summary of recent works on dust production is included. last, we conclude with a discussion of the observational constraints and potential future advances for study into these stars on the low mass/high mass star boundary. | super-agb stars and their role as electron capture supernova progenitors |
this book surveys our understanding of stars which change in brightness because they pulsate. pulsating variable stars are keys to distance scales inside and beyond the milky way galaxy. they test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the milky way and other local group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail. | pulsating stars |
we currently know about 30 magnetars: seemingly isolated neutron stars whose properties can be (in part) comprehended only acknowledging that they are endowed with magnetic fields of complex morphology and exceptional intensity-at least in some components of the field structure. although magnetars represent only a small percentage of the known isolated neutron stars, there are almost certainly many more of them, since most magnetars were discovered in transitory phases called outbursts, during which they are particularly noticeable. in outburst, in fact, a magnetar can be brighter in x-rays by orders of magnitude and usually emit powerful bursts of hard-x/soft-gamma-ray photons that can be detected almost everywhere in the galaxy with all-sky monitors such as those on board the fermi satellite or the neil gehrels swift observatory. magnetars command great attention because the large progress that has been made in their understanding is proving fundamental to fathom the whole population of isolated neutron stars, and because, due to their extreme properties, they are relevant for a vast range of different astrophysical topics, from the study of gamma-ray bursts and superluminous supernovae, to ultraluminous x-ray sources, fast radio bursts, and even to sources of gravitational waves. several excellent reviews with different focuses were published on magnetars in the last few years: among others, israel and dall'osso (2011); rea and esposito (2011); turolla and esposito (2013); mereghetti et al. (2015); turolla et al. (2015); kaspi and beloborodov (2017). here, we quickly recall the history of these sources and travel through the main observational facts, trying to touch some recent and sometimes little-discussed ramifications of magnetars. | magnetars: a short review and some sparse considerations |
we report on a set of long-term general-relativistic three-dimensional (3d) multi-group (energy-dependent) neutrino radiation-hydrodynamics simulations of core-collapse supernovae. we employ a full 3d two-moment scheme with the local m1 closure, three neutrino species, and 12 energy groups per species. with this, we follow the post-core-bounce evolution of the core of a nonrotating 27 - {m}⊙progenitor in full unconstrained 3d and in octant symmetry for ≳380 ms. we find the development of an asymmetric runaway explosion in our unconstrained simulation. we test the resolution dependence of our results and, in agreement with previous work, find that low resolution artificially aids explosion and leads to an earlier runaway expansion of the shock. at low resolution, the octant and full 3d dynamics are qualitatively very similar, but at high resolution, only the full 3d simulation exhibits the onset of explosion. | general-relativistic three-dimensional multi-group neutrino radiation-hydrodynamics simulations of core-collapse supernovae |
understanding gravitational wave emission from core-collapse supernovae will be essential for their detection with current and future gravitational wave detectors. this requires a sample of waveforms from modern 3d supernova simulations reaching well into the explosion phase, where gravitational wave emission is expected to peak. however, recent waveforms from 3d simulations with multigroup neutrino transport do not reach far into the explosion phase, and some are still obtained from non-exploding models. we therefore calculate waveforms up to 0.9 s after bounce using the neutrino hydrodynamics code coconut-fmt. we consider two models with low and normal explosion energy, namely explosions of an ultra-stripped progenitor with an initial helium star mass of 3.5 m_{⊙}, and of an 18 m_{⊙} single star. both models show gravitational wave emission from the excitation of surface g modes in the proto-neutron star with frequencies between ∼800 and 1000 hz at peak emission. the peak amplitudes are about 6 and 10 cm, respectively, which is somewhat higher than in most recent 3d models of the pre-explosion or early explosion phase. using a bayesian analysis, we determine the maximum detection distances for our models in simulated advanced ligo, advanced virgo, and einstein telescope (et) design sensitivity noise. the more energetic 18 m_{⊙} explosion will be detectable to about 17.5 kpc by the ligo/virgo network and to about 180 kpc with the et. | gravitational wave emission from 3d explosion models of core-collapse supernovae with low and normal explosion energies |
we investigate the impact of the nonzero neutrino splitting and elastic neutrino-nucleon collisions on fast neutrino oscillations. our calculations confirm that a small neutrino mass splitting and the neutrino mass hierarchy have very little effect on fast oscillation waves. we also demonstrate explicitly that fast oscillations remain largely unaffected for the time/distance scales that are much smaller than the neutrino mean free path but are damped on larger scales. this damping originates from both the direct modification of the dispersion relation of the oscillation waves in the neutrino medium and the flattening of the neutrino angular distributions over time. our work suggests that fast neutrino oscillation waves produced near the neutrino sphere can propagate essentially unimpeded which may have ramifications in various aspects of the supernova physics. | fast flavor oscillations in dense neutrino media with collisions |
magnetorotational supernovae are a rare type of core-collapse supernovae where the magnetic field and rotation play a central role in the dynamics of the explosion. we present the post-processed nucleosynthesis of state-of-the-art neutrino-mhd supernova models that follow the post explosion evolution for few seconds. we find three different dynamical mechanisms to produce heavy r-process elements: (i) a prompt ejection of matter right after core bounce, (ii) neutron-rich matter that is ejected at late times due to a reconfiguration of the protoneutronstar shape, (iii) small amount of mass ejected with high entropies in the centre of the jet. we investigate total ejecta yields, including the ones of unstable nuclei such as 26al, 44ti, 56ni, and 60fe. the obtained 56ni masses vary between $0.01\!-\!1\, \mathrm{m_\odot }$. the latter maximum is compatible with hypernova observations. furthermore, all of our models synthesize zn masses in agreement with observations of old metal-poor stars. we calculate simplified light curves to investigate whether our models can be candidates for superluminous supernovae. the peak luminosities obtained from taking into account only nuclear heating reach up to a few $\sim 10^{43} \, \mathrm{erg\, s^{-1}}$. under certain conditions, we find a significant impact of the 66ni decay chain that can raise the peak luminosity up to $\sim 38{{\ \rm per \, cent}}$ compared to models including only the 56ni decay chain. this work reinforces the theoretical evidence on the critical role of magnetorotational supernovae to understand the occurrence of hypernovae, superluminous supernovae, and the synthesis of heavy elements. | magnetorotational supernovae: a nucleosynthetic analysis of sophisticated 3d models |
we consider an axion-like particle (alp) coupled to standard model (sm) fermions as a mediator between the sm and a fermionic dark matter (dm) particle. we explore the case where the alp-sm and/or the alp-dm couplings are too small to allow for dm generation via standard freeze-out. dm is therefore thermally decoupled from the visible sector and must be generated through either freeze-in or decoupled freeze-out (dfo). in the dfo regime, we present an improved approach to obtain the relic density by solving a set of three stiff coupled boltzmann equations, one of which describes the energy transfer from the sm to the dark sector. having determined the region of parameter space where the correct relic density is obtained, we revisit experimental constraints from electron beam dump experiments, rare b and k decays, exotic higgs decays at the lhc, astrophysics, dark matter searches and cosmology. in particular, for our specific alp scenario we (re) calculate and improve beam dump, flavour and supernova constraints. throughout our calculation we implement state-of-the-art chiral perturbation theory results for the alp partial decay width to hadrons. we find that while the dfo region, which predicts extremely small alp-fermion couplings, can probably only be constrained by cosmological observables, the freeze-in region covers a wide area of parameter space that may be accessible to other more direct probes. some of this parameter space is already excluded, but a significant part should be accessible to future collider experiments. | axion-like particles as mediators for dark matter: beyond freeze-out |
new feebly interacting particles would emerge from a supernova core with 100-mev-range energies and produce γ rays by subsequent decays. these would contribute to the diffuse cosmic γ -ray background or would have shown up in the solar maximum mission satellite from sn 1987a. however, we show for the example of axionlike particles that, even at distances beyond the progenitor star, the decay photons may not escape and can instead form a fireball, a plasma shell with t ≲1 mev . thus, existing arguments do not exclude axionlike particles with few 10 mev masses and a two-photon coupling of a few 10-10 gev-1 . however, the energy would have showed up in sub-mev photons, which were not seen from sn 1987a in the pioneer venus orbiter, closing again this new window. a careful reassessment is required for other particles that were constrained in similar ways. | axion-sourced fireballs from supernovae |
one of the active debates in core-collapse supernova (ccsn) theory is how significantly neutrino flavor conversions induced by neutrino-neutrino self-interactions change the conventional picture of ccsn dynamics. recent studies have indicated that strong flavor conversions can occur inside neutrino spheres where neutrinos are tightly coupled to matter. these flavor conversions are associated with either collisional instability or fast neutrino-flavor conversion (ffc) or both. the impact of these flavor conversions on ccsn dynamics is, however, still highly uncertain due to the lack of global simulations of quantum kinetic neutrino transport with appropriate microphysical inputs. given fluid profiles from a recent ccsn model at three different time snapshots in the early postbounce phase, we perform global-quantum kinetic simulations in spherical symmetry with an essential set of microphysics. we find that strong flavor conversions occur in optically thick regions, resulting in a substantial change of neutrino radiation field. the neutrino heating in the gain region is smaller than the case with no flavor conversions, whereas the neutrino cooling in the optically thick region is commonly enhanced. based on the neutrino data obtained from our multiangle neutrino transport simulations, we also assess some representative classical closure relations by applying them to diagonal components of density matrix of neutrinos. we find that eddington tensors can be well-approximated by these closure relations except for the region where flavor conversions occur vividly. we also analyze the neutrino signal by carrying out detector simulations for super-kamiokande, dune, and juno. we propose a useful strategy to identify the sign of flavor conversions in neutrino signal, that can be easily implemented in real data analyses of ccsn neutrinos. | basic characteristics of neutrino flavor conversions in the postshock regions of core-collapse supernova |
we present new cosmological constraints in a set of motivated extensions of the $\lambda$cdm model using the polarization and gravitational lensing measurements from the south pole telescope and the planck cmb temperature observations at large angular scales. in all cosmological scenarios, this cmb data brings the clustering measurements into agreement with the low-redshift probes of large-scale structure. combining the spt-3g, sptpol and planck large-scale temperature data with the latest full-shape boss and bao measurements, information from the weak lensing and photometric galaxy clustering, and pantheon supernova set we find a $4\sigma$ evidence for nonzero neutrino mass, $\sum m_\nu=0.22\pm0.06\,{\rm ev}$.breaking the cmb degeneracies between $\sum m_\nu$ and the cosmological parameters by the boss data is a major contribution to our neutrino mass measurement. the future cmb data would allow for investigating this measurement. then we explore the possibility of dynamical dark energy with two model-independent approaches: one introduces a phantom crossing in dark energy equation of state, another provides with a sharp transition in the dark energy evolution. for the combination of all data considered, the both models predict $h_0\simeq68\,{\rm km\,s^{-1}mpc^{-1}}$ being in a $\sim3\sigma$ tension with the sh0es constraint. however, when the local type ia supernovae are calibrated by cepheids, the late universe scenarios suggest significantly higher values of $h_0$ consistent with sh0es. our work draws attention to the supernova absolute magnitude calibration as one of the issues on the way to reconcile the $h_0$ tension. | exploring ${\\lambda}$cdm extensions with spt-3g and planck data: 4$\\sigma$ evidence for neutrino masses and implications of extended dark energy models for cosmological tensions |
we investigate the constraint ability of the gravitational wave (gw) as the standard siren on the cosmological parameters by using the third-generation gravitational wave detector: the einstein telescope. the binary merger of a neutron with either a neutron or black hole is hypothesized to be the progenitor of a short and intense burst of γ rays; some fraction of those binary mergers could be detected both through electromagnetic radiation and gravitational waves. thus we can determine both the luminosity distance and redshift of the source separately. we simulate the luminosity distances and redshift measurements from 100 to 1000 gw events. we use two different algorithms to constrain the cosmological parameters. for the hubble constant h0 and dark matter density parameter ωm, we adopt the markov chain monte carlo approach. we find that with about 500-600 gw events we can constrain the hubble constant with an accuracy comparable to planck temperature data and planck lensing combined results, while for the dark matter density, gws alone seem not able to provide the constraints as good as for the hubble constant; the sensitivity of 1000 gw events is a little lower than that of planck data. it should require more than 1000 events to match the planck sensitivity. yet, for analyzing the more complex dynamical property of dark energy, i.e., the equation of state w , we adopt a new powerful nonparametric method: the gaussian process. we can reconstruct w directly from the observational luminosity distance at every redshift. in the low redshift region, we find that about 700 gw events can give the constraints of w (z ) comparable to the constraints of a constant w by planck data with type-ia supernovae. those results show that gws as the standard sirens to probe the cosmological parameters can provide an independent and complementary alternative to current experiments. | estimating cosmological parameters by the simulated data of gravitational waves from the einstein telescope |
the zwicky transient facility (ztf) has discovered five events (0.01 < z < 0.4) belonging to an emerging class of active galactic nuclei (agns) undergoing smooth, large-amplitude, and rapidly rising flares. this sample consists of several transients initially classified as supernovae with narrow spectral lines. however, upon closer inspection, all of the host galaxies display balmer lines with fwhm(hβ) ~ 900-1400 km s-1, characteristic of a narrow-line seyfert 1 (nlsy1) galaxy. the transient events are long lived, over 400 days on average in the observed frame. we report uv and x-ray follow-up of the flares and observe persistent uv emission, with two of the five transients detected with luminous x-ray emission, ruling out a supernova interpretation. we compare the properties of this sample to previously reported flaring nlsy1 galaxies and find that they fall into three spectroscopic categories: 1) balmer line profiles and fe ii complexes typical of nlsy1s, 2) strong he ii profiles, and 3) he ii profiles including bowen fluorescence features. the latter are members of the growing class of agn flares attributed to enhanced accretion reported by trakhtenbrot et al. we consider physical interpretations in the context of related transients from the literature. for example, two of the sources show high-amplitude rebrightening in the optical, ruling out a simple tidal disruption event scenario for those transients. we conclude that three of the sample belong to the trakhtenbrot et al. class and two are tidal disruption events in nlsy1s. we also hypothesize as to why nlsy1s are preferentially the sites of such rapid enhanced flaring activity. | a family tree of optical transients from narrow-line seyfert 1 galaxies |
we develop a hybrid model of galactic chemical evolution that combines a multiring computation of chemical enrichment with a prescription for stellar migration and the vertical distribution of stellar populations informed by a cosmological hydrodynamic disc galaxy simulation. our fiducial model adopts empirically motivated forms of the star formation law and star formation history, with a gradient in outflow mass loading tuned to reproduce the observed metallicity gradient. with this approach, the model reproduces many of the striking qualitative features of the milky way disc's abundance structure: (i) the dependence of the [o/fe]-[fe/h] distribution on radius rgal and mid-plane distance |z|; (ii) the changing shapes of the [o/h] and [fe/h] distributions with rgal and |z|; (iii) a broad distribution of [o/fe] at sub-solar metallicity and changes in the [o/fe] distribution with rgal, |z|, and [fe/h]; (iv) a tight correlation between [o/fe] and stellar age for [o/fe] > 0.1; (v) a population of young and intermediate-age α-enhanced stars caused by migration-induced variability in the type ia supernova rate; (vi) non-monotonic age-[o/h] and age-[fe/h] relations, with large scatter and a median age of ~4 gyr near solar metallicity. observationally motivated models with an enhanced star formation rate ~2 gyr ago improve agreement with the observed age-[fe/h] and age-[o/h] relations, but worsen agreement with the observed age-[o/fe] relation. none of our models predict an [o/fe] distribution with the distinct bimodality seen in the observations, suggesting that more dramatic evolutionary pathways are required. all code and tables used for our models are publicly available through the versatile integrator for chemical evolution (vice; https://pypi.org/project/vice). | stellar migration and chemical enrichment in the milky way disc: a hybrid model |
we study the implications of the planck temperature power spectrum at low multipoles, 0l<100, and sptpol data. we show that this combination predicts consistent lensing-induced smoothing of acoustic peaks within λcdm cosmology and yields the robust predictions of the cosmological parameters. combining only the planck large-scale temperature data and the sptpol polarization and lensing measurements within λcdm model we found substantially lower values of linear matter density perturbation σ8 which bring the late-time parameter s8=σ8√ωm/0.3=0.763±0.022 into accordance with galaxy clustering and weak lensing measurements. it also raises up the hubble constant h0=69.68±1.00kms that reduces the hubble tension to the 2.5σ level. we examine the residual tension in the early dark energy (ede) model which produces the brief energy injection prior to recombination. we implement both the background and perturbation evolutions of the scalar field which potential scales as v(phi)propto phi2n. including cosmic shear measurements (kids, viking-450, des) and local distance-ladder data (sh0es) to the combined fit we found that ede completely alleviates the hubble tension while not degradating the fit to large-scale structure data. the ede scenario significantly improves the goodness-of-fit by 2.9σ in comparison with the concordance λcdm model. the account for the intermediate-redshift data (the supernova dataset and baryon acoustic oscillation data) fits perfectly to our parameter predictions and indicates the preference of ede over λcdm at 3σ. | combined analysis of planck and sptpol data favors the early dark energy models |
a dense neutrino gas, such as the one anticipated in the supernova environment, can experience fast neutrino flavor conversions on scales much shorter than those expected in vacuum probably provided that the angular distributions of νe and ν¯e cross each other. we perform a detailed investigation of the neutrino angular distributions obtained by solving the boltzmann equations for fixed matter profiles of some representative snapshots during the postbounce phase of core-collapse supernovae in multidimensional calculations of a 11.2 m⊙ and a 27 m⊙ progenitor model. although the 11.2 m⊙ model features νe-ν¯e angular crossings and the associated fast modes at different time snapshots, the 27 m⊙ model does not show any crossings within the decoupling region. we show that this can be understood by studying the multipole components of the neutrino distributions. in fact, there is a higher chance for the occurrence of νe-ν¯e angular crossings for the zones where the multipole components of the neutrino distributions are strong enough. we also show that there can exist more than one crossing between the angular distributions of νe and ν¯e. in addition, apart from the crossings within the neutrino decoupling region, there is a class of νe-ν¯e angular crossings that appears very deep inside the protoneutron star. | fast neutrino flavor conversion modes in multidimensional core-collapse supernova models: the role of the asymmetric neutrino distributions |
the observed tension (∼9% difference) between the local distance ladder measurement of the hubble constant, h0, and its value inferred from the cosmic microwave background could hint at new, exotic, cosmological physics. we test the impact of the assumption about the expansion history of the universe ( $0.01\lt z\lt 2.3$ ) on the local distance ladder estimate of h0. in the fiducial analysis, the hubble flow type ia supernova (sn ia) sample is truncated to z < 0.15, and the deceleration parameter (q0) is fixed to -0.55. we create realistic simulations of the calibrator and pantheon samples, and account for a full systematics covariance between these two sets. we fit several physically motivated dark-energy models, and derive combined constraints from calibrator and pantheon sne ia and simultaneously infer h0 and dark-energy properties. we find that the assumption on the dark-energy model does not significantly change the local distance ladder value of h0, with a maximum difference (δh0) between the inferred value for different models of 0.47 km ${{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ , i.e., a 0.6% shift in h0, significantly smaller than the observed tension. additional freedom in the dark-energy models does not increase the error in the inferred value of h0. including systematics covariance between the calibrators, low-redshift sne, and high-redshift sne can induce small shifts in the inferred value for h0. the sn ia systematics in this study contribute ≲0.8% to the total uncertainty of h0. | cosmological model insensitivity of local h0 from the cepheid distance ladder |
we present results from the semi-analytic model of galaxy formation sagapplied on the multidark simulation mdpl2. sag features an updated supernova (sn) feedback scheme and a robust modelling of the environmental effects on satellite galaxies. this incorporates a gradual starvation of the hot gas halo driven by the action of ram pressure stripping (rps), that can affect the cold gas disc, and tidal stripping (ts), which can act on all baryonic components. galaxy orbits of orphan satellites are integrated providing adequate positions and velocities for the estimation of rps and ts. the star formation history and stellar mass assembly of galaxies are sensitive to the redshift dependence implemented in the sn feedback model. we discuss a variant of our model that allows to reconcile the predicted star formation rate density at z ≳ 3 with the observed one, at the expense of an excess in the faint end of the stellar mass function at z= 2. the fractions of passive galaxies as a function of stellar mass, halo mass, and the halo-centric distances are consistent with observational measurements. the model also reproduces the evolution of the main sequence of star-forming central and satellite galaxies. the similarity between them is a result of the gradual starvation of the hot gas halo suffered by satellites, in which rps plays a dominant role. rps of the cold gas does not affect the fraction of quenched satellites but it contributes to reach the right atomic hydrogen gas content for more massive satellites (m⋆ ≳ 1010 m⊙). | semi-analytic galaxies - i. synthesis of environmental and star-forming regulation mechanisms |
we study diffusive shock acceleration (dsa) of protons and electrons at nonrelativistic, high mach number, quasiparallel, collisionless shocks by means of self-consistent 1d particle-in-cell simulations. for the first time, both species are found to develop power-law distributions with the universal spectral index -4 in momentum space, in agreement with the prediction of dsa. we find that scattering of both protons and electrons is mediated by right-handed circularly polarized waves excited by the current of energetic protons via nonresonant hybrid (bell) instability. protons are injected into dsa after a few gyrocycles of shock drift acceleration (sda), while electrons are first preheated via sda, then energized via a hybrid acceleration process that involves both sda and fermi-like acceleration mediated by bell waves, before eventual injection into dsa. using the simulations we can measure the electron-proton ratio in accelerated particles, which is of paramount importance for explaining the cosmic ray fluxes measured on earth and the multiwavelength emission of astrophysical objects such as supernova remnants, radio supernovae, and galaxy clusters. we find the normalization of the electron power law is ≲1 0-2 of the protons for strong nonrelativistic shocks. | simultaneous acceleration of protons and electrons at nonrelativistic quasiparallel collisionless shocks |
massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. we present here the $z\sim 6\mbox{--}8$ candidate high-redshift galaxies from the reionization lensing cluster survey (relics), a hubble and spitzer space telescope survey of 41 massive galaxy clusters spanning an area of ≈200 arcmin2. these clusters were selected to be excellent lenses, and we find similar high-redshift sample sizes and magnitude distributions as the cluster lensing and supernova survey with hubble (clash). we discover 257, 57, and eight candidate galaxies at z ∼ 6, 7, and 8 respectively, (322 in total). the observed (lensed) magnitudes of the z ∼ 6 candidates are as bright as ab mag ∼23, making them among the brightest known at these redshifts, comparable with discoveries from much wider, blank-field surveys. relics demonstrates the efficiency of using strong gravitational lenses to produce high-redshift samples in the epoch of reionization. these brightly observed galaxies are excellent targets for follow-up study with current and future observatories, including the james webb space telescope. | relics: the reionization lensing cluster survey and the brightest high-z galaxies |
we implement a multigroup and discrete-ordinate neutrino transport model in spherical symmetry which allows to simulate collective neutrino oscillations by including realistic collisional rates in a self-consistent way. we utilize this innovative model, based on strategic parameter rescaling, to study a recently proposed collisional flavor instability caused by the asymmetry of emission and absorption rates between νe and ν¯ e for four different static backgrounds taken from different stages in a core-collapse supernova simulation. our results confirm that collisional instabilities generally exist around the neutrinosphere during the supernova accretion and postaccretion phase, as suggested by johns [arxiv:2104.11369.]. however, the growth and transport of flavor instabilities can only be fully captured by models with global simulations as done in this work. with minimal ingredient to trigger collisional instabilities, we find that the flavor oscillations and transport mainly affect (anti)neutrinos of heavy lepton flavors around their decoupling sphere, which then leave imprints on their energy spectra in the free-streaming regime. for electron (anti)neutrinos, their properties remain nearly intact. we also explore various effects due to the decoherence from neutrino-nucleon scattering, artificially enhanced decoherence from emission and absorption, neutrino vacuum mixing, and inhomogeneous matter profile, and discuss the implication of our work. | evolution of collisional neutrino flavor instabilities in spherically symmetric supernova models |
we present extensive optical photometry of the afterglow of grb 221009a. our data cover 0.9-59.9 days from the time of swift and fermi gamma-ray burst (grb) detections. photometry in rizy-band filters was collected primarily with pan-starrs and supplemented by multiple 1-4 m imaging facilities. we analyzed the swift x-ray data of the afterglow and found a single decline rate power law f(t) ∝ t -1.556±0.002 best describes the light curve. in addition to the high foreground milky way dust extinction along this line of sight, the data favor additional extinction to consistently model the optical to x-ray flux with optically thin synchrotron emission. we fit the x-ray-derived power law to the optical light curve and find good agreement with the measured data up to 5-6 days. thereafter we find a flux excess in the riy bands that peaks in the observer frame at ~20 days. this excess shares similar light-curve profiles to the type ic broad-lined supernovae sn 2016jca and sn 2017iuk once corrected for the grb redshift of z = 0.151 and arbitrarily scaled. this may be representative of an sn emerging from the declining afterglow. we measure rest-frame absolute peak ab magnitudes of mg= -19.8 ± 0.6 and mr= - 19.4 ± 0.3 and mz= -20.1 ± 0.3. if this is an sn component, then bayesian modeling of the excess flux would imply explosion parameters of ${m}_{\mathrm{ej}}={7.1}_{-1.7}^{+2.4}$ m ⊙, ${m}_{\mathrm{ni}}={1.0}_{-0.4}^{+0.6}$ m ⊙, and ${v}_{\mathrm{ej}}={{\rm{33,900}}}_{-5700}^{+5900}$ km s-1, for the ejecta mass, nickel mass, and ejecta velocity respectively, inferring an explosion energy of e kin ≃ 2.6-9.0 × 1052 erg. | the optical light curve of grb 221009a: the afterglow and the emerging supernova |
we examine the formation of dark matter (dm) cores in dwarf galaxies simulated with the eagle model of galaxy formation. as in earlier work, we find that the star formation (sf) gas density threshold (ρth) plays a critical role. at low thresholds (lt), gas is unable to reach densities high enough to dominate the gravitational potential before being dispersed by feedback from supernovae. lt runs show little effect on the inner dm profile, even in systems with extended and bursty sf, two ingredients often cited as critical for core formation. for higher thresholds, gas is able to dominate the gravitational potential before being ejected by feedback. this can lead to a substantial reduction in the inner dm content, but only if the gas is gravitationally important over an extended period of time, allowing the halo to contract before gas removal. rapid assembly and removal of gas in short sf bursts is less effective at altering the inner dm content. subsequent gas accretion may draw dm back in and reform a cusp, unless sf is bursty enough to prevent it, preserving the core. thus, for the eagle sf + feedback model, there is no simple relation between core formation and sf history, contrary to recent claims. the dependence of the inner dm content of dwarfs on ρth hinders robust predictions and the interpretation of observations. a simulation of a (12 mpc)^3 volume with high ρth results in dwarfs with sizeable cores over a limited halo mass range, but with insufficient variety in mass profiles to explain the observed diversity of dwarf galaxy rotation curves. | baryon-induced dark matter cores in the eagle simulations |
we present detailed submillimeter- through centimeter-wave observations of the extraordinary extragalactic transient at2018cow. the apparent characteristics—the high radio luminosity, the rise and long-lived emission plateau at millimeter bands, and the sub-relativistic velocity—have no precedent. a basic interpretation of the data suggests {e}k≳ 4 × {10}48 {erg} coupled to a fast but sub-relativistic (v≈ 0.13c) shock in a dense ({n}e≈ 3 × {10}5 {cm}}-3) medium. we find that the x-ray emission is not naturally explained by an extension of the radio-submm synchrotron spectrum, nor by inverse compton scattering of the dominant blackbody uv/optical/ir photons by energetic electrons within the forward shock. by {{δ }}t≈ 20 {days}, the x-ray emission shows spectral softening and erratic inter-day variability. taken together, we are led to invoke an additional source of x-ray emission: the central engine of the event. regardless of the nature of this central engine, this source heralds a new class of energetic transients shocking a dense medium, which at early times are most readily observed at millimeter wavelengths. | at2018cow: a luminous millimeter transient |
we study the effects of cosmic rays (crs) on outflows from star-forming galaxies in the circum and intergalactic medium (cgm/igm), in high-resolution, fully cosmological fire-2 simulations (accounting for mechanical and radiative stellar feedback, magnetic fields, anisotropic conduction/viscosity/cr diffusion and streaming, and cr losses). we showed previously that massive ($m_{\rm halo}\gtrsim 10^{11}\, \mathrm{m}_{\odot }$), low-redshift (z ≲ 1-2) haloes can have cr pressure dominate over thermal cgm pressure and balance gravity, giving rise to a cooler cgm with an equilibrium density profile. this dramatically alters outflows. absent crs, high gas thermal pressure in massive haloes 'traps' galactic outflows near the disc, so they recycle. with crs injected in supernovae as modelled here, the low-pressure halo allows 'escape' and cr pressure gradients continuously accelerate this material well into the igm in 'fast' outflows, while lower-density gas at large radii is accelerated in situ into 'slow' outflows that extend to >mpc scales. cgm/igm outflow morphologies are radically altered: they become mostly volume-filling (with inflow in a thin mid-plane layer) and coherently biconical from the disc to >mpc. the cr-driven outflows are primarily cool ($t\sim \! 10^{5}\,$ k) and low velocity. all of these effects weaken and eventually vanish at lower halo masses ($\lesssim 10^{11}\, \mathrm{m}_{\odot }$) or higher redshifts (z ≳ 1-2), reflecting the ratio of cr to thermal + gravitational pressure in the outer halo. we present a simple analytical model that explains all of the above phenomena. we caution that these predictions may depend on uncertain cr transport physics. | cosmic ray driven outflows to mpc scales from l* galaxies |
we present an analysis of the quenching of star formation in galaxies, bulges, and disks throughout the bulk of cosmic history, from z = 2 − 0. we utilise observations from the sloan digital sky survey and the mapping nearby galaxies at apache point observatory survey at low redshifts. we complement these data with observations from the cosmic assembly near-infrared deep extragalactic legacy survey at high redshifts. additionally, we compare the observations to detailed predictions from the lgalaxies semi-analytic model. to analyse the data, we developed a machine learning approach utilising a random forest classifier. we first demonstrate that this technique is extremely effective at extracting causal insight from highly complex and inter-correlated model data, before applying it to various observational surveys. our primary observational results are as follows: at all redshifts studied in this work, we find bulge mass to be the most predictive parameter of quenching, out of the photometric parameter set (incorporating bulge mass, disk mass, total stellar mass, and b/t structure). moreover, we also find bulge mass to be the most predictive parameter of quenching in both bulge and disk structures, treated separately. hence, intrinsic galaxy quenching must be due to a stable mechanism operating over cosmic time, and the same quenching mechanism must be effective in both bulge and disk regions. despite the success of bulge mass in predicting quenching, we find that central velocity dispersion is even more predictive (when available in spectroscopic data sets). in comparison to the lgalaxies model, we find that all of these observational results may be consistently explained through quenching via preventative `radio-mode' active galactic nucleus feedback. furthermore, many alternative quenching mechanisms (including virial shocks, supernova feedback, and morphological stabilisation) are found to be inconsistent with our observational results and those from the literature. | the quenching of galaxies, bulges, and disks since cosmic noon. a machine learning approach for identifying causality in astronomical data |
we have performed a multiwavelength study of supernova remnant (snr) g57.2+0.8 and its environment. the snr hosts the magnetar sgr 1935+2154, which emitted an extremely bright millisecond-duration radio burst on 2020 april 28. we used the 12co and 13co j = 1-0 data from the milky way image scroll painting co line survey to search for molecular gas associated with g57.2+0.8, in order to constrain the physical parameters (e.g., the distance) of the snr and its magnetar. we report that snr g57.2+0.8 is likely impacting the molecular clouds (mcs) at the local standard of rest (lsr) velocity ${v}_{\mathrm{lsr}}\sim 30\,\mathrm{km}\,{{\rm{s}}}^{-1}$ and excites a weak 1720 mhz oh maser with a peak flux density of 47 mjy beam-1. the chance coincidence of a random oh spot falling in the snr is ≤12%, and the oh-co correspondence chance is 7% at the maser spot. this combines to give <1% false probability of the oh maser, suggesting a real maser detection. the lsr velocity of the mcs places the snr and magnetar at a kinematic distance of 6.6 ± 0.7 kpc. the nondetection of thermal x-ray emission from the snr and the relatively dense environment suggests g57.2+0.8 be an evolved snr with an age $t\gtrsim 1.6\times {10}^{4}(d/6.6\,\,\mathrm{kpc})\,\,\mathrm{yr}$ . the explosion energy of g57.2+0.8 is lower than $2\times {10}^{51}{({n}_{0}/10{\mathrm{cm}}^{-3})}^{1.16}{(d/6.6\mathrm{kpc})}^{3.16}\,\mathrm{erg}$ , which is not very energetic even assuming a high ambient density ${n}_{0}=10\,\,{\mathrm{cm}}^{-3}$ . this reinforces the opinion that magnetars do not necessarily result from very energetic supernova explosions. | revisiting the distance, environment, and supernova properties of snr g57.2+0.8 that hosts sgr 1935+2154 |
the discrepancy between the values of the hubble constant h0 derived from the local distance ladder and the cosmic microwave background provides a tantalizing hint of new physics. we explore a potential resolution involving screened fifth forces in the local universe, which alter the cepheid calibration of supernova distances. in particular, if the cepheids with direct distance measurements from parallax or water masers are screened but a significant fraction of those in other galaxies are not, neglecting the difference between their underlying period-luminosity relations biases the local h0 measurement high. this difference derives from a reduction in the cepheid pulsation period and possible increase in luminosity under a fifth force. we quantify the internal and environmental gravitational properties of the riess et al. distance ladder galaxies to assess their degrees of screening under a range of phenomenological models, and propagate this information into the h0 posterior as a function of fifth force strength. we consider well-studied screening models in scalar-tensor gravity theories such as chameleon, k-mouflage and vainshtein, along with a recently-proposed mechanism based on baryon-dark matter interactions in which screening is governed by the local dark matter density. we find that a fifth force strength ∼5 %- 30 % that of gravity can alleviate the h0 tension in many scenarios, around the sensitivity level at which tests based on other distance ladder data can constrain this strength. our most successful models achieve consistency with planck at the ∼1.5 σ level. although our analysis is exploratory and based on screening models that are not necessarily realized in full theories, our results demonstrate that new physics-based local resolutions of the h0 tension are possible, supplementing those already known in the prerecombination era. | local resolution of the hubble tension: the impact of screened fifth forces on the cosmic distance ladder |
we place observational constraints on the galileon ghost condensate model, a dark energy proposal in cubic-order horndeski theories consistent with the gravitational-wave event gw170817. the model extends the covariant galileon by taking an additional higher-order field derivative x2 into account. this allows for the dark energy equation of state wde to access the region -2 <wde<-1 without ghosts. indeed, this peculiar evolution of wde is favored over that of the cosmological constant λ from the joint data analysis of cosmic microwave background (cmb) radiation, baryonic acoustic oscillations (baos), supernovae type ia (snia), and redshift-space distortions (rsds). furthermore, our model exhibits a better compatibility with the cmb data over the λ -cold-dark-matter (λ cdm ) model by suppressing large-scale temperature anisotropies. the cmb temperature and polarization data lead to an estimation for today's hubble parameter h0 consistent with its direct measurements at 2 σ . we perform a model selection analysis by using several methods and find a statistically significant preference of the galileon ghost condensate model over λ cdm . | cosmological data favor galileon ghost condensate over λ cdm |
we present very early, high-cadence photometric observations of the nearby type ia sn 2017cbv. the light curve is unique in that it has a blue bump during the first five days of observations in the u, b, and g bands, which is clearly resolved given our photometric cadence of 5.7 hr during that time span. we model the light curve as the combination of early shocking of the supernova ejecta against a nondegenerate companion star plus a standard sn ia component. our best-fit model suggests the presence of a subgiant star 56 r ⊙ from the exploding white dwarf, although this number is highly model-dependent. while this model matches the optical light curve well, it overpredicts the observed flux in the ultraviolet bands. this may indicate that the shock is not a blackbody, perhaps because of line blanketing in the uv. alternatively, it could point to another physical explanation for the optical blue bump, such as interaction with circumstellar material or an unusual nickel distribution. early optical spectra of sn 2017cbv show strong carbon (c ii λ6580) absorption up through day -13 with respect to maximum light, suggesting that the progenitor system contains a significant amount of unburned material. these early results on sn 2017cbv illustrate the power of early discovery and intense follow-up of nearby supernovae to resolve standing questions about the progenitor systems and explosion mechanisms of sne ia. | early blue excess from the type ia supernova 2017cbv and implications for its progenitor |
this paper introduces a new approach to reconstruct cosmological functions using artificial neural networks based on observational measurements with minimal theoretical and statistical assumptions. by using neural networks, we can generate computational models of observational datasets, and then we compare them with the original ones to verify the consistency of our method. this methodology is applicable to even small-size datasets. in particular, we test the proposed method with data coming from cosmic chronometers, f σ8 measurements, and the distance modulus of the type ia supernovae. furthermore, we introduce a first approach to generate synthetic covariance matrices through a variational autoencoder, using the systematic covariance matrix of the type ia supernova compilation. | neural network reconstructions for the hubble parameter, growth rate and distance modulus |
most massive stars, the progenitors of core-collapse supernovae, are in close binary systems and may interact with their companion through mass transfer or merging. we undertake a population synthesis study to compute the delay-time distribution of core-collapse supernovae, that is, the supernova rate versus time following a starburst, taking into account binary interactions. we test the systematic robustness of our results by running various simulations to account for the uncertainties in our standard assumptions. we find that a significant fraction, %, of core-collapse supernovae are "late", that is, they occur 50-200 myr after birth, when all massive single stars have already exploded. these late events originate predominantly from binary systems with at least one, or, in most cases, with both stars initially being of intermediate mass (4-8 m⊙). the main evolutionary channels that contribute often involve either the merging of the initially more massive primary star with its companion or the engulfment of the remaining core of the primary by the expanding secondary that has accreted mass at an earlier evolutionary stage. also, the total number of core-collapse supernovae increases by % because of binarity for the same initial stellar mass. the high rate implies that we should have already observed such late core-collapse supernovae, but have not recognized them as such. we argue that φ persei is a likely progenitor and that eccentric neutron star - white dwarf systems are likely descendants. late events can help explain the discrepancy in the delay-time distributions derived from supernova remnants in the magellanic clouds and extragalactic type ia events, lowering the contribution of prompt ia events. we discuss ways to test these predictions and speculate on the implications for supernova feedback in simulations of galaxy evolution. | delay-time distribution of core-collapse supernovae with late events resulting from binary interaction |
we present the gravitational waveforms computed in ab initio two-dimensional core collapse supernova models evolved with the chimera code for progenitor masses between 12 and 25 m⊙ . all models employ multifrequency neutrino transport in the ray-by-ray approximation, state-of-the-art weak interaction physics, relativistic transport corrections such as the gravitational redshift of neutrinos, two-dimensional hydrodynamics with the commensurate relativistic corrections, newtonian self-gravity with a general-relativistic monopole correction, and the lattimer-swesty equation of state with 220 mev compressibility, and begin with the most recent woosley-heger nonrotating progenitors in this mass range. all of our models exhibit robust explosions. therefore, our waveforms capture all stages of supernova development: 1) a relatively short and weak prompt signal, 2) a quiescent stage, 3) a strong signal due to convection and standing accretion shock instability activity, 4) termination of active accretion onto the proto-neutron star, and 5) a slowly increasing tail that reaches a saturation value. fourier decomposition shows that the gravitational wave signals we predict should be observable by advligo for galactic events across the range of progenitors considered here. the fundamental limitation of these models is in their imposition of axisymmetry. further progress will require counterpart three-dimensional models, which are underway. | gravitational wave signatures of ab initio two-dimensional core collapse supernova explosion models for 12 -25 m⊙ stars |
the hot (>106 k) phase of the circumgalactic medium (cgm) contains a large fraction of baryons in galaxies. it also retains signatures of the processes that shaped the galaxies, such as feedback from active galactic nuclei and supernovae, and offers a uniquely powerful way to constrain theoretical models of feedback. it is, however, notoriously difficult to detect. by stacking 2643 optically selected galaxies in the erosita final equatorial depth survey, we present spatially resolved properties of the extended cgm in both star-forming and quiescent galaxies spanning an order of magnitude in stellar mass. we mask out resolved point sources and galaxy groups/clusters and model the contribution from x-ray binaries and the hot interstellar medium, producing accurate radial profiles. we compare the profiles to mock x-ray observations of galaxy stacks in the illustristng100 and eagle cosmological simulations. we detect extended emission from both the high-mass ( $10.7\lt \mathrm{log}({m}_{* }/{m}_{\odot })\lt 11.2$ ) and low-mass ( $10.2\lt \mathrm{log}({m}_{* }/{m}_{\odot })\lt 10.7$ ) galaxy stacks. galaxies have somewhat more luminous cgm between 10 and 100 kpc if they are more massive or star-forming. however, the luminosity increases more slowly with stellar mass than predicted in simulations. simulated quenched galaxies are dimmer than observed, suggesting that they rely too heavily on cgm ejection for quenching. star-forming galaxies are observed to have flatter and more extended profiles than in simulations, suggesting underefficient stellar feedback models. our results highlight the need to modify future prescriptions of galaxy feedback models. | testing galaxy feedback models with resolved x-ray profiles of the hot circumgalactic medium |
determining the differential-rotation law of compact stellar objects produced in binary neutron stars mergers or core-collapse supernovae is an old problem in relativistic astrophysics. addressing this problem is important because it impacts directly on the maximum mass these objects can attain and, hence, on the threshold to black-hole formation under realistic conditions. using the results from a large number of numerical simulations in full general relativity of binary neutron star mergers described with various equations of state and masses, we study the rotational properties of the resulting hypermassive neutron stars. we find that the angular-velocity distribution shows only a modest dependence on the equation of state, thus exhibiting the traits of "quasiuniversality" found in other aspects of compact stars, both isolated and in binary systems. the distributions are characterized by an almost uniformly rotating core and a "disk." such a configuration is significantly different from the j -constant differential-rotation law that is commonly adopted in equilibrium models of differentially rotating stars. furthermore, the rest-mass contained in such a disk can be quite large, ranging from ≃0.03 m⊙ in the case of high-mass binaries with stiff equations of state, up to ≃0.2 m⊙ for low-mass binaries with soft equations of state. we comment on the astrophysical implications of our findings and on the long-term evolutionary scenarios that can be conjectured on the basis of our simulations. | rotational properties of hypermassive neutron stars from binary mergers |
the combination of multiple observational probes has long been advocated as a powerful technique to constrain cosmological parameters, in particular dark energy. the dark energy survey has measured 207 spectroscopically confirmed type ia supernova light curves, the baryon acoustic oscillation feature, weak gravitational lensing, and galaxy clustering. here we present combined results from these probes, deriving constraints on the equation of state, w , of dark energy and its energy density in the universe. independently of other experiments, such as those that measure the cosmic microwave background, the probes from this single photometric survey rule out a universe with no dark energy, finding w =-0.8 0-0.11+0.09. the geometry is shown to be consistent with a spatially flat universe, and we obtain a constraint on the baryon density of ωb=0.06 9-0.012+0.009 that is independent of early universe measurements. these results demonstrate the potential power of large multiprobe photometric surveys and pave the way for order of magnitude advances in our constraints on properties of dark energy and cosmology over the next decade. | cosmological constraints from multiple probes in the dark energy survey |
the hypothetical massive dark photon (γ‧) which has kinetic mixing with the sm photon can decay electromagnetically to e+e- pairs if its mass m exceeds 2me, and otherwise into three sm photons. these decays yield cosmological and supernovae associated signatures. we briefly discuss these signatures, particularly in connection with the supernova sn1987a, and delineate the extra constraints that arise on the mass and mixing parameter of the dark photon. in particular, we find that for dark photon mass mγ‧ in the 5-20 mev range arguments based on supernova 1987a observations lead to a bound on ɛ which is about 300 times stronger than the presently existing bounds based on energy loss arguments. | supernova bounds on the dark photon using its electromagnetic decay |
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