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We present EXplosive TRAnsient Spectral Simulator (extrass), a newly developed code aimed at generating 3D spectra for supernovae in the nebular phase by using modern multidimensional explosion models as input. It is well established that supernovae are asymmetric by nature, and that the morphology is encoded in the line profiles during the nebular phase, months after the explosion. In this work, we use extrass to study one such simulation of a $3.3\, \mathrm{ M}_\odot$ He-core explosion ($M_\text{ejecta}=1.3\, M_\odot$, $E_\text{kin}=1.05\times 10^{51}\,$erg) modelled with the Prometheus-HotB code and evolved to the homologous phase. Our code calculates the energy deposition from the radioactive decay of 56Ni → 56Co → 56Fe and uses this to determine the Non-Local-Thermodynamic-Equilibrium temperature, excitation, and ionization structure across the nebula. From the physical condition solutions we generate the emissivities to construct spectra depending on viewing angles. Our results show large variations in the line profiles with viewing angles, as diagnosed by the first three moments of the line profiles; shifts, widths, and skewness. We compare line profiles from different elements, and study the morphology of line-of-sight slices that determine the flux at each part of a line profile. We find that excitation conditions can sometimes make the momentum vector of the ejecta emitting in the excited states significantly different from that of the bulk of the ejecta of the respective element, thus giving blueshifted lines for bulk receding material, and vice versa. We compare the 3.3 M⊙ He-core model to observations of the Type Ib supernova SN 2007Y.

Thermal bombs are a widely used method to artificially trigger explosions of core-collapse supernovae (CCSNe) to determine their nucleosynthesis or ejecta and remnant properties. Recently, their use in spherically symmetric (1D) hydrodynamic simulations led to the result that {56,57}Ni and 44Ti are massively underproduced compared to observational estimates for Supernova 1987A, if the explosions are slow, i.e., if the explosion mechanism of CCSNe releases the explosion energy on long timescales. It was concluded that rapid explosions are required to match observed abundances, i.e., the explosion mechanism must provide the CCSN energy nearly instantaneously on timescales of some ten to order 100 ms. This result, if valid, would disfavor the neutrino-heating mechanism, which releases the CCSN energy on timescales of seconds. Here, we demonstrate by 1D hydrodynamic simulations and nucleosynthetic post-processing that these conclusions are a consequence of disregarding the initial collapse of the stellar core in the thermal-bomb modelling before the bomb releases the explosion energy. We demonstrate that the anti-correlation of 56Ni yield and energy-injection timescale vanishes when the initial collapse is included and that it can even be reversed, i.e., more 56Ni is made by slower explosions, when the collapse proceeds to small radii similar to those where neutrino heating takes place in CCSNe. We also show that the 56Ni production in thermal-bomb explosions is sensitive to the chosen mass cut and that a fixed mass layer or fixed volume for the energy deposition cause only secondary differences. Moreover, we propose a most appropriate setup for thermal bombs., 24 pages, 12 figures; version accepted by MNRAS after minor revision

SN 2020cxd is a representative of the family of low-energy, underluminous Type IIP supernovae (SNe), whose observations and analysis were recently reported by Yang et al. (2021). Here we re-evaluate the observational data for the diagnostic SN properties by employing the hydrodynamic explosion model of a 9 MSun red supergiant progenitor with an iron core and a pre-collapse mass of 8.75 Msun. The explosion of the star was obtained by the neutrino-driven mechanism in a fully self-consistent simulation in three dimensions (3D). Multi-band light curves and photospheric velocities for the plateau phase are computed with the one-dimensional radiation-hydrodynamics code STELLA, applied to the spherically averaged 3D explosion model as well as spherisized radial profiles in different directions of the 3D model. We find that the overall evolution of the bolometric light curve, duration of the plateau phase, and basic properties of the multi-band emission can be well reproduced by our SN model with its explosion energy of only 0.7x10^50 erg and an ejecta mass of 7.4 Msun. These values are considerably lower than the previously reported numbers, but they are compatible with those needed to explain the fundamental observational properties of the prototype low-luminosity SN 2005cs. Because of the good compatibility of our photospheric velocities with line velocities determined for SN 2005cs, we conclude that the line velocities of SN 2020cxd are probably overestimated by up to a factor of about 3. The evolution of the line velocities of SN 2005cs compared to photospheric velocities in different explosion directions might point to intrinsic asymmetries in the SN ejecta., 13 pages + Appendix, 9 figures, accepted for publication in MNRAS

We explore the impact of small-scale flavor conversions of neutrinos, the so-called fast flavor conversions (FFCs), on the dynamical evolution and neutrino emission of core-collapse supernovae (CCSNe). In order to do that, we implement FFCs in the spherically symmetric (1D) CCSN simulations of a 20 solar-mass progenitor model parametrically, assuming that FFCs happen at densities lower than a systematically varied threshold value and lead to an immediate flavor equilibrium consistent with lepton number conservation. We find that besides hardening the electron neutrino and antineutrino spectra, which helps the expansion of the shock by enhanced postshock heating, FFCs can cause significant, nontrivial modifications of the energy transport in the SN environment via increasing the heavy-lepton neutrino luminosities. In our non-exploding models this results in extra cooling of the layers around the neutrinospheres, which triggers a faster contraction of the proto-neutron star and hence, in our 1D models, hampers the CCSN explosion. Although our study is limited by the 1D nature of our simulations, it provides valuable insights into how neutrino flavor conversions in the deepest CCSN regions can impact the neutrino release and the corresponding response of the stellar medium., Comment: 20 pages, 10 figures, slightly extended version, accepted by PRD

The outflows from neutrino-cooled black-hole (BH) accretion disks formed in neutron-star mergers or cores of collapsing stars are expected to be neutron-rich enough to explain a large fraction of elements created by the rapid neutron-capture (r-) process, but their precise chemical composition remains elusive. Here, we investigate the role of fast neutrino flavor conversion, motivated by the findings of our post-processing analysis that shows evidence of electron-neutrino lepton-number (ELN) crossings deep inside the disk, hence suggesting possibly non-trivial effects due to neutrino flavor mixing. We implement a parametric, dynamically self-consistent treatment of fast conversion in time-dependent simulations and examine the impact on the disk and its outflows. By activating the, otherwise inefficient, emission of heavy-lepton neutrinos, fast conversions enhance the disk cooling rates and reduce the absorption rates of electron-type neutrinos, causing a reduction of the electron fraction in the disk by 0.03-0.06 and in the ejected material by 0.01-0.03. The r-process yields are enhanced by typically no more than a factor of two, rendering the overall impact of fast conversions modest. The kilonova is prolonged as a net result of increased lanthanide opacities and enhanced radioactive heating rates. We observe only mild sensitivity to the disk mass, the condition for the onset of flavor conversion, and to the considered cases of flavor mixing. Remarkably, parametric models of flavor mixing that conserve the lepton numbers per family result in an overall smaller impact than models invoking three-flavor equipartition, often assumed in previous works., 25 pages, 10 figures, 1 table; accepted to PRD

The hot and dense core formed in the collapse of a massive star is a powerful source of hypothetical feebly-interacting particles such as sterile neutrinos, dark photons, axion-like particles (ALPs), and others. Radiative decays such as $a\to2\gamma$ deposit this energy in the surrounding material if the mean free path is less than the radius of the progenitor star. For the first time, we use a supernova (SN) population with particularly low explosion energies as the most sensitive calorimeters to constrain this possibility. These SNe are observationally identified as low-luminosity events with low ejecta velocities and low masses of ejected $^{56}$Ni. Their low energies limit the energy deposition from particle decays to less than about 0.1 B, where $1~{\rm B~(bethe)}=10^{51}~{\rm erg}$. For 1-500 MeV-mass ALPs, this generic argument excludes ALP-photon couplings $G_{a\gamma\gamma}$ in the $10^{-10}$-$10^{-8}~{\rm GeV}^{-1}$ range., Comment: 5+3 pages, 2+2 figures. Minor modifications added; version published in Physical Review Letters

We present a coherent study of the impact of neutrino interactions on the r-process element nucleosynthesis and the heating rate produced by the radioactive elements synthesised in the dynamical ejecta of neutron star-neutron star (NS-NS) mergers. We have studied the material ejected from four NS-NS merger systems based on hydrodynamical simulations which handle neutrino effects in an elaborate way by including neutrino equilibration with matter in optically thick regions and re-absorption in optically thin regions. We find that the neutron richness of the dynamical ejecta is significantly affected by the neutrinos emitted by the post-merger remnant, in particular when compared to a case neglecting all neutrino interactions. Our nucleosynthesis results show that a solar-like distribution of r- process elements with mass numbers $A \gtrsim 90$ is produced, including a significant enrichment in Sr and a reduced production of actinides compared to simulations without inclusion of the nucleonic weak processes. The composition of the dynamically ejected matter as well as the corresponding rate of radioactive decay heating are found to be rather independent of the system mass asymmetry and the adopted equation of state. This approximate degeneracy in abundance pattern and heating rates can be favourable for extracting the ejecta properties from kilonova observations, at least if the dynamical component dominates the overall ejecta. Part II of this work will study the light curve produced by the dynamical ejecta of our four NS merger models., 18 pages, 21 figures, 2 Tables, accepted by MNRAS 2021-11-19

Following our recent work on Type II supernovae (SNe), we present a set of 1D nonlocal thermodynamic equilibrium radiative transfer calculations for nebular-phase Type Ibc SNe starting from state-of-the-art explosion models with detailed nucleosynthesis. Our grid of progenitor models is derived from He stars that were subsequently evolved under the influence of wind mass loss. These He stars, which most likely form through binary mass exchange, synthesize less oxygen than their single-star counterparts with the same zero-age main sequence (ZAMS) mass. This reduction is greater in He-star models evolved with an enhanced mass loss rate. We obtain a wide range of spectral properties at 200d. In models from He stars with an initial mass >6Msun, the [OI] 6300, 6364 is of comparable or greater strength than [CaII] 7291,7323 -- the strength of [OI] 6300, 6364 increases with He-star initial mass. In contrast, models from lower mass He stars exhibit a weak [OI] 6300, 6364, strong [CaII] 7291,7323, but also strong NII lines and FeII emission below 5500A. The ejecta density, modulated by the ejecta mass, the explosion energy, and clumping, has a critical impact on the gas ionization, line cooling, and the spectral properties. FeII dominates the emission below 5500A and is stronger at earlier nebular epochs. It ebbs as the SN ages, while the fractional flux in [OI] 6300, 6364 and [CaII] 7291,7323 increases, with a similar rate, as the ejecta recombine. Although the results depend on the adopted wind mass loss rate and pre-SN mass, we find that He stars of 6-8Msun initially (ZAMS mass of 23-28Msun) match adequately the properties of standard SNe Ibc. Our results for less massive He stars are more perplexing, since the predicted spectra are not seen in nature. They may be missed by current surveys or associated with Type Ibn SNe in which interaction dominates over decay power. [Abridged], Accepted for publication in A&A

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 possibly generic spin-kick alignment has been interpreted as indication that NS spins are either induced with the NS kicks or inherited from 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. In contrast, the NS spins are only determined minutes to hours later by angular momentum associated with 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 onesided 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., 38 pages, 9 figures, 1 table; includes new Sect.2 summarizing observations and new Fig. 8; considerably extended because of comments by referee and readers; accepted by ApJ

Stars in the mass range from 8 to 10 solar masses are expected to produce one of two types of supernovae (SNe), either electron-capture supernovae (ECSNe) or core-collapse supernovae (CCSNe), depending on their previous evolution. Either of the associated progenitors retain extended and massive hydrogen-rich envelopes, the observables of these SNe are, therefore, expected to be similar. In this study we explore the differences in these two types of SNe. Specifically, we investigate three different progenitor models: a solar-metallicity ECSN progenitor with an initial mass of 8.8 solar masses, a zero-metallicity progenitor with 9.6 solar masses, and a solar-metallicity progenitor with 9 solar masses, carrying out radiative transfer simulations for these progenitors. We present the resulting light curves for these models. The models exhibit very low photospheric velocity variations of about 2000 km/s, therefore, this may serve as a convenient indicator of low-mass SNe. The ECSN has very unique light curves in broad bands, especially the U band, and does not resemble any currently observed SN. This ECSN progenitor being part of a binary will lose its envelope for which reason the light curve becomes short and undetectable. The SN from the 9.6 solar masses progenitor exhibits also quite an unusual light curve, explained by the absence of metals in the initial composition. The artificially iron polluted 9.6 solar masses model demonstrates light curves closer to normal SNe IIP. The SN from the 9 solar masses progenitor remains the best candidate for so-called low-luminosity SNe IIP like SN 1999br and SN 2005cs., 19 pages, 19 figures. Accepted by MNRAS

We present a set of nonlocal thermodynamic equilibrium steady-state calculations of radiative transfer for one-year old type II supernovae (SNe) starting from state-of-the-art explosion models computed with detailed nucleosynthesis. This grid covers single-star progenitors with initial masses between 9 and 29$M_{\odot}$, all evolved with KEPLER at solar metallicity and ignoring rotation. The [OI]$\lambda\lambda$$6300,6364$ line flux generally grows with progenitor mass, and H$\alpha$ exhibits an equally strong and opposite trend. The [CaII]$\lambda\lambda$$7291,\,7323$ strength increases at low $^{56}$Ni mass, low explosion energy, or with clumping. This CaII doublet, which forms primarily in the explosively-produced Si/S zones, depends little on the progenitor mass, but may strengthen if Ca$^+$ dominates in the H-rich emitting zones or if Ca is abundant in the O-rich zones. Indeed, Si-O shell merging prior to core collapse may boost the CaII doublet at the expense of the OI doublet, and may thus mimic the metal line strengths of a lower mass progenitor. We find that the $^{56}$Ni bubble effect has a weak impact, probably because it is too weak to induce much of an ionization shift in the various emitting zones. Our simulations compare favorably to observed SNe II, including SN2008bk (e.g., 9$M_{\odot}$ model), SN2012aw (12$M_{\odot}$ model), SN1987A (15$M_{\odot}$ model), or SN2015bs (25$M_{\odot}$ model with no Si-O shell merging). SNe II with narrow lines and a low $^{56}$Ni mass are well matched by the weak explosion of 9$-$11$M_{\odot}$ progenitors. The nebular-phase spectra of standard SNe II can be explained with progenitors in the mass range 12$-$15$M_{\odot}$, with one notable exception for SN2015bs. In the intermediate mass range, these mass estimates may increase by a few $M_{\odot}$ with allowance for clumping of the O-rich material or CO molecular cooling., Comment: Accepted for publication in A&A

The diffuse cosmic supernova neutrino background (DSNB) is observational target of the gadolinium-loaded Super-Kamiokande (SK) detector and the forthcoming JUNO and Hyper-Kamiokande detectors. Current predictions are hampered by our still incomplete understanding of the supernova (SN) explosion mechanism and of the neutron star (NS) equation of state and maximum mass. In our comprehensive study we revisit this problem on grounds of the landscapes of successful and failed SN explosions obtained by Sukhbold et al. and Ertl et al. with parametrized one-dimensional neutrino engines for large sets of single-star and helium-star progenitors, with the latter serving as proxy of binary evolution effects. Besides considering engines of different strengths, leading to different fractions of failed SNe with black-hole (BH) formation, we also vary the NS mass limit, the spectral shape of the neutrino emission, and include contributions from poorly understood alternative NS-formation channels such as accretion-induced or merger-induced collapse events. Since the neutrino signals of our large model sets are approximate, we calibrate the associated degrees of freedom by using state-of-the-art simulations of proto-neutron star cooling. Our predictions are higher than other recent ones because of a large fraction of failed SNe with long delay to BH formation. Our best-guess model predicts a DSNB electron-antineutrino-flux of 28.8^{+24.6}_{-10.9} cm^{-2}s^{-1} with 6.0^{+5.1}_{-2.1} cm^{-2}s^{-1} in the favorable measurement interval of [10,30] MeV, and 1.3^{+1.1}_{-0.4} cm^{-2}s^{-1} with electron-antineutrino energies > 17.3 MeV, which is roughly a factor of two below the current SK limit. The uncertainty range is dominated by the still insufficiently constrained cosmic rate of stellar core-collapse events., 43 pages, 16 figures, 10 tables; revised version with new Sections 6 & 9, and new Appendix E; accepted by ApJ

Invited talk presented at the ''NuPhys2019: Prospects in Neutrino Physics'' &nbsp

We present 3D hydrodynamic simulations of neutrino-driven supernovae (SNe) with the PROMETHEUS-HOTB code, evolving the asymmetrically expanding ejecta from shock breakout until they reach the homologous expansion phase after roughly one year. Our calculations continue the simulations for two red supergiant (RSG) and two blue supergiant (BSG) progenitors by Wongwathanarat et al., who investigated the growth of explosion asymmetries produced by hydrodynamic instabilities during the first second of the explosion and their later fragmentation by Rayleigh-Taylor instabilities. We focus on the late time acceleration and inflation of the ejecta caused by the heating due to the radioactive decay of $^{56}$Ni to $^{56}$Fe and by a new outward-moving shock, which forms when the reverse shock from the He/H-shell interface compresses the central part of the ejecta. The mean velocities of the iron-rich ejecta increase between 100 km/s and 350 km/s ($\sim$8-30\%), and the fastest one percent of the iron accelerates by up to $\sim$1000 km/s ($\sim$20-25\%). This 'Ni-bubble effect', known from 1D models, accelerates the bulk of the nickel in our 3D models and causes an inflation of the initially overdense Ni-rich clumps, which leads to underdense, extended fingers, enveloped by overdense skins of compressed surrounding matter. We also provide volume and surface filling factors as well as a spherical harmonics analysis to characterize the spectrum of Ni-clump sizes quantitatively. Three of our four models give volume filling factors larger than 0.3, consistent with what is suggested for SN 1987A by observations., 30 pages, 22 figures, 6 tables, extended discussion of correlation of late and initial explosion asymmetries, accepted by MNRAS

Neutrinos are unique probes of core-collapse supernova dynamics, especially in the case of black hole (BH) forming stellar collapses, where the electromagnetic emission may be faint or absent. By investigating two 3D hydrodynamical simulations of BH-forming stellar collapses of mass 40 and 75 M_sun, we identify the physical processes preceding BH formation through neutrinos, and forecast the neutrino signal expected in the existing IceCube and Super-Kamiokande detectors, as well as in the future generation DUNE facility. Prior to the abrupt termination of the neutrino signal corresponding to BH formation, both models develop episodes of strong and long-lasting activity by the spiral standing accretion shock instability (SASI). We find that the spiral SASI peak in the Fourier power spectrum of the neutrino event rate will be distinguishable at 3 sigma above the detector noise for distances up to O(30) kpc in the most optimistic scenario, with IceCube having the highest sensitivity. Interestingly, given the long duration of the spiral SASI episodes, the spectrograms of the expected neutrino event rate carry clear signs of the evolution of the blue spiral SASI frequency as a function of time, as the shock radius and post-shock fluid velocity evolve. Due to the high accretion luminosity and its large-amplitude SASI-induced modulations, any contribution from asymmetric (dipolar or quadrupolar) neutrino emission associated with the lepton emission self-sustained asymmetry (LESA) is far subdominant in the neutrino signal., Comment: 25 pages, including 19 figures. Discussion on LESA expanded; conclusions unchanged. Matches version accepted for publication in Phys. Rev. D. Animated visualizations available at: https://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Walk2019/

The possible detection of a compact object in the remnant of SN 1987A presents an unprecedented opportunity to follow its early evolution. The suspected detection stems from an excess of infrared emission from a dust blob near the compact object's predicted position. The infrared excess could be due to the decay of isotopes like 44Ti, accretion luminosity from a neutron star or black hole, magnetospheric emission or a wind originating from the spindown of a pulsar, or thermal emission from an embedded, cooling neutron star (NS 1987A). It is shown that the last possibility is the most plausible as the other explanations are disfavored by other observations and/or require fine-tuning of parameters. Not only are there indications the dust blob overlaps the predicted location of a kicked compact remnant, but its excess luminosity also matches the expected thermal power of a 30 year old neutron star. Furthermore, models of cooling neutron stars within the Minimal Cooling paradigm readily fit both NS 1987A and Cas A, the next-youngest known neutron star. If correct, a long heat transport timescale in the crust and a large effective stellar temperature are favored, implying relatively limited crustal n-1S0 superfluidity and an envelope with a thick layer of light elements, respectively. If the locations don't overlap, then pulsar spindown or accretion might be more likely, but the pulsar's period and magnetic field or the accretion rate must be rather finely tuned. In this case, NS 1987A may have enhanced cooling and/or a heavy-element envelope., Comment: 21 pages, 6 figures, to be published in ApJ

Neutrinos emitted in the coalescence of two neutron stars affect the dynamics of the outflow ejecta and the nucleosynthesis of heavy elements. In this work, we analyze the neutrino emission properties and the conditions leading to the growth of flavor instabilities in merger remnants consisting of a hypermassive neutron star and an accretion disk during the first 10 ms after the merger. The analyses are based on hydrodynamical simulations that include a modeling of neutrino emission and absorption effects via the "Improved Leakage-Equilibration-Absorption Scheme" (ILEAS). We also examine the nucleosynthesis of the heavy elements via the rapid neutron-capture process (r-process) inside the material ejected during this phase. The dominant emission of $\bar\nu_e$ over $\nu_e$ from the merger remnant leads to favorable conditions for the occurrence of fast pairwise flavor conversions of neutrinos, independent of the chosen equation of state or the mass ratio of the binary. The nucleosynthesis outcome is very robust, ranging from the first to the third r-process peaks. In particular, more than $10^{-5}$ $M_\odot$ of strontium are produced in these early ejecta that may account for the GW170817 kilonova observation. We find that the amount of ejecta containing free neutrons after the $r$-process freeze-out, which may power early-time UV emission, is reduced by roughly a factor of 10 when compared to simulations that do not include weak interactions. Finally, the potential flavor equipartition between all neutrino flavors is mainly found to affect the nucleosynthesis outcome in the polar ejecta within $\lesssim 30^\circ$, by changing the amount of the produced iron-peak and first-peak nuclei, but it does not alter the lanthanide mass fraction therein., Comment: matches the published version

Abridged. We aim at exploring to which extent the remnant keeps memory of the asymmetries that develop stochastically in the neutrino-heating layer due to hydrodynamic instabilities (e.g., convective overturn and the standing accretion shock instability) during the first second after core bounce. We coupled a 3D HD model of a neutrino-driven SN explosion with 3D MHD/HD simulations of the remnant formation. The simulations cover 2000 years of expansion and include all physical processes relevant to describe the complexities in the SN evolution and the subsequent interaction of the stellar debris with the wind of the progenitor star. The interaction of large-scale asymmetries left from the earliest phases of the explosion with the reverse shock produces, at the age of $\approx 350$~years, an ejecta structure and a remnant morphology which are remarkably similar to those observed in Cas A. Small-scale structures in the large-scale Fe-rich plumes created during the initial stages of the SN, combined with HD instabilities that develop after the passage of the reverse shock, naturally produce a pattern of ring- and crown-like structures of shocked ejecta. The consequence is a spatial inversion of the ejecta layers with Si-rich ejecta being physically interior to Fe-rich ejecta. The full-fledged remnant shows voids and cavities in the innermost unshocked ejecta resulting from the expansion of Fe-rich plumes and their inflation due to the decay of radioactive species. The asymmetric distributions of $^{44}$Ti and $^{56}$Fe and their abundance ratio are both compatible with those inferred from high-energy observations of Chandra and NuSTAR. The main asymmetries observed in the ejecta distribution of Cas A can be explained by the interaction of the reverse shock with the large-scale asymmetries that developed from stochastic processes that originate during the first seconds of the SN blast., Comment: 33 pages, 29 figures, 1 Table, 4 movies, 3 interactive graphics, accepted for publication on A&A, high quality figures will be available on the published paper

The mass function for black holes and neutron stars at birth is explored for mass-losing helium stars. These should resemble, more closely than similar studies of single hydrogen-rich stars, the results of evolution in close binary systems. The effects of varying the mass-loss rate and metallicity are calculated using a simple semi-analytic approach to stellar evolution that is tuned to reproduce detailed numerical calculations. Though the total fraction of black holes made in stellar collapse events varies considerably with metallicity, mass-loss rate, and mass cutoff, from 5$\%$ to 30$\%$, the shapes of their birth functions are very similar for all reasonable variations in these quantities. Median neutron star masses are in the range 1.32 - 1.37 $M_\odot$ regardless of metallicity. The median black hole mass for solar metallicity is typically 8 to 9 $M_\odot$ if only initial helium cores below 40 $M_\odot$ (ZAMS mass less than 80 $M_\odot$) are counted, and 9 - 13 $M_\odot$, in most cases, if helium cores with initial masses up to 150 $M_\odot$ (ZAMS mass less than 300 $M_\odot$) contribute. As long as the mass-loss rate as a function of mass exhibits no strong non-linearities, the black hole birth function from 15 to 35 $M_\odot$ has a slope that depends mostly on the initial mass function for main sequence stars. These findings imply the possibility of constraining the initial mass function and the properties of mass loss in close binaries using ongoing measurements of gravitational wave radiation. The expected rotation rates of the black holes are briefly discussed., Comment: submitted to ApJ

The high temperature and electron degeneracy attained during a supernova allow for the formation of a large muon abundance within the core of the resulting proto-neutron star. If new pseudoscalar degrees of freedom have large couplings to the muon, they can be produced by this muon abundance and contribute to the cooling of the star. By generating the largest collection of supernova simulations with muons to date, we show that observations of the cooling rate of SN 1987A place strong constraints on the coupling of axion-like particles to muons, limiting the coupling to $g_{a��} < 10^{-7.5}~\text{GeV}^{-1}$., 8 pages, 9 figures. v6: Consolidated version with various errors corrected and the discussion clarified

We present 3D full-sphere supernova simulations of non-rotating low-mass (~9 Msun) progenitors, covering the entire evolution from core collapse through bounce and shock revival, through shock breakout from the stellar surface, until fallback is completed several days later. We obtain low-energy explosions [~(0.5-1.0)x 10^{50} erg] of iron-core progenitors at the low-mass end of the core-collapse supernova (LMCCSN) domain and compare to a super-AGB (sAGB) progenitor with an oxygen-neon-magnesium core that collapses and explodes as electron-capture supernova (ECSN). The onset of the explosion in the LMCCSN models is modelled self-consistently using the Vertex-Prometheus code, whereas the ECSN explosion is modelled using parametric neutrino transport in the Prometheus-HOTB code, choosing different explosion energies in the range of previous self-consistent models. The sAGB and LMCCSN progenitors that share structural similarities have almost spherical explosions with little metal mixing into the hydrogen envelope. A LMCCSN with less 2nd dredge-up results in a highly asymmetric explosion. It shows efficient mixing and dramatic shock deceleration in the extended hydrogen envelope. Both properties allow fast nickel plumes to catch up with the shock, leading to extreme shock deformation and aspherical shock breakout. Fallback masses of 40 km/s and a NS spin period of ~30 ms, both not largely different from those of the Crab pulsar at birth., Comment: 47 pages, 27 figures, 6 tables; minor revisions, accepted by MNRAS

We present spherically symmetric (1D) and axisymmetric (2D) supernova simulations for a convection-dominated 9 Msun and a 20 Msun progenitor that develops violent activity by the standing-accretion-shock instability (SASI). We compare in detail the Aenus-Alcar code, which uses fully multidimensional two-moment neutrino transport with an M1 closure, with a ray-by-ray-plus (RbR+) version of this code and with the Prometheus-Vertex code that employs RbR+ two-moment transport with a Boltzmann closure. Besides testing consequences of ignored non-radial neutrino-flux components in the RbR+ approximation, we also discuss the influence of various transport ingredients applied or not applied in recent literature, namely simplified neutrino-pair processes, neutrino-electron scattering, velocity-dependent and gravitational-redshift terms, and strangeness and many-body corrections for neutrino-nucleon scattering. Alcar and Vertex show excellent agreement in 1D and 2D despite a slightly but systematically smaller radius (~1km) and stronger convection of the proto-neutron star with Alcar. As found previously, the RbR+ approximation is conducive to explosions, but much less severely in the convection-dominated 9 Msun case than in the marginally exploding 20 Msun model, where the onset time of explosion also exhibits big stochastic variations, and the RbR+ approximation has no distinctly stronger supportive effect than simplified pair processes or strangeness and many-body corrections. Neglecting neutrino-electron scattering has clearly unfavorable effects for explosions, while ignoring velocity and gravitational-redshift effects can both promote or delay the explosion. The ratio of advection timescale to neutrino-heating timescale in 1D simulations is a sensitive indicator of the influence of physics ingredients on explosions also in multidimensional simulations., 32 pages, 15 figures, accepted to MNRAS, extended the ray-by-ray analysis and final discussion compared to version 1, results remain unchanged

Recently, first neutrino-driven supernova explosions have been obtained in 3D, self-consistent, first-principle simulations, these models are still not always exploding robustly and, in general, the explosions are not sufficiently energetic. To constrain the explosion mechanism, and the related uncertainties, it is thus very helpful to consider observational constraints: pulsar kicks, progenitor association and supernova remnants (SNR). Recent observations of asymmetries in the supernova ejecta of Cas A are very promising, to compare to long-term simulations of the explosion. In addition 3D observations of SN87A are becoming more constraining on the geometry of the ejected material during the explosion. In this talk I will discuss our efforts to model the late time evolution of a 3D supernova explosion, where we include the effects of beta decay, which inflates the structures rich in 56Ni. The structures we find in the simulations depend on the quantities plotted.

During the first few hundred days after the explosion, core-collapse supernovae (SNe) emit down-scattered X-rays and gamma-rays originating from radioactive line emissions, primarily from the $^{56}$Ni $\rightarrow$ $^{56}$Co $\rightarrow$ $^{56}$Fe chain. We use SN models based on three-dimensional neutrino-driven explosion simulations of single stars and mergers to compute this emission and compare the predictions with observations of SN 1987A. A number of models are clearly excluded, showing that high-energy emission is a powerful way of discriminating between models. The best models are almost consistent with the observations, but differences that cannot be matched by a suitable choice of viewing angle are evident. Therefore, our self-consistent models suggest that neutrino-driven explosions are able to produce, in principle, sufficient mixing, although remaining discrepancies may require small changes to the progenitor structures. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor envelope. The main effect of asymmetries is to vary the flux level by a factor of ${\sim}$3. For the more asymmetric models, the shapes of the light curves also change. In addition to the models of SN 1987A, we investigate two models of Type II-P SNe and one model of a stripped-envelope Type IIb SN. The Type II-P models have similar observables as the models of SN 1987A, but the stripped-envelope SN model is significantly more luminous and evolves faster. Finally, we make simple predictions for future observations of nearby SNe., 27 pages, 12 figures. Accepted for publication in ApJ. Updated to match the accepted version; added two paragraphs in Section 2 on differences between the models/the level of mixing and rephrased the NuSTAR predictions slightly

We present a carefully designed, systematic study of the angular resolution dependence of simulations with the Prometheus-Vertex neutrino-hydrodynamics code. Employing a simplified neutrino heating-cooling scheme in the Prometheus hydrodynamics module allows us to sample the angular resolution between 4 degrees and 0.5 degrees. With a newly-implemented static mesh refinement (SMR) technique on the Yin-Yang grid, the angular coordinates can be refined in concentric shells, compensating for the diverging structure of the spherical grid. In contrast to previous studies with Prometheus and other codes, we find that higher angular resolution and therefore lower numerical viscosity provides more favorable explosion conditions and faster shock expansion. We discuss the possible reasons for the discrepant results. The overall dynamics seem to converge at a resolution of about 1 degree. Applying the SMR setup to marginally exploding progenitors is disadvantageous for the shock expansion, however, because kinetic energy of downflows is dissipated to internal energy at resolution interfaces, leading to a loss of turbulent pressure support and a steeper temperature gradient. We also present a way to estimate the numerical viscosity on grounds of the measured turbulent kinetic-energy spectrum, leading to smaller values that are better compatible with the flow behavior witnessed in our simulations than results following calculations in previous literature. Interestingly, the numerical Reynolds numbers in the turbulent, neutrino-heated postshock layer (some 10 to several 100) are in the ballpark of expected neutrino-drag effects on the relevant length scales in the turbulent postshock layer. We provide a formal derivation and quantitative assessment of the neutrino drag terms in an appendix., 37 pages, 14 figures, 4 tables; revised version with neutrino drag discussion extended for numerical evaluation; accepted by ApJ

The neutrino process that occurs in the outer stellar shells during a supernova explosion and involves neutrino-nucleus reactions produces a range of rare, stable and radioactive isotopes. We improve previous $\nu$-process studies by using, for the first time, the time-dependent neutrino emission spectra, as predicted from supernova simulations, rather than a simplified parametric description modeled after the neutron-star cooling phase. In particular, our calculations use time-dependent neutrino spectra for all neutrino species, consider their deviation from a Fermi-Dirac distribution and account for the neutrino emission from the neutrino burst and accretion phases. We find that the time-dependent treatment of the neutrino emission spectra results in higher yields for the selected nuclei produced by the $\nu$~process as compared to previous studies and also compared to the approximation of assuming constant neutrino energies corresponding to the time-averaged mean energy radiated in each species. The effect is largest for nuclides produced by charged-current reactions. Our results reflect the dynamical competition between neutrino-induced reactions and the effect of the shock passage through the star. By varying the neutrino burst luminosity and the duration of the accretion phase, we study the impact of these early emission phases and their uncertainties on the $\nu$-process nucleosynthesis. We find that the deviation of the neutrino spectra from a Fermi-Dirac distribution calculated in supernova simulations has a negligible effect on the $\nu$-process yields., Comment: 16 pages, 8 figures, 2 tables, submitted to the Astrophysical Journal

We describe a multi-messenger interpretation of GW170817, which yields a robust lower limit on NS radii. This excludes NSs with radii smaller than about 10.7 km and thus rules out very soft nuclear matter. We stress the potential of this type of constraints when future detections become available. A very similar argumentation may yield an upper bound on the maximum mass of nonrotating NSs. We also discuss simulations of NS mergers, which undergo a first-order phase transition to quark matter. We point out a different dynamical behavior. Considering the gravitational-wave signal, we identify an unambiguous signature of the QCD phase transition in NS mergers. The occurrence of quark matter through a strong first-order phase transition during merging leads to a characteristic shift of the dominant postmerger frequency. The frequency shift is indicative for a phase transition if it is compared to the postmerger frequency which is expected for purely hadronic EoS models. A very strong deviation of several 100 Hz is observed for hybrid EoSs in an otherwise tight relation between the tidal deformability and the postmerger frequency. We address the potential impact of a first-order phase transition on the electromagnetic counterpart of NS mergers. Our simulations suggest that there would be no significant qualitative differences between a system undergoing a phase transition to quark matter and purely hadronic mergers. The quantitative differences are within the spread which is found between different hadronic EoS models. This implies on the one hand that GW170817 is compatible with a possible transition to quark matter. On the other hand these considerations show that it may not be easy to identify quantitative differences between purely hadronic mergers and events in which quark matter occurs considering solely their electromagnetic counterpart or their nucleosynthesis products. (abridged), Comment: 15 pages, 11 figures, submitted to the AIP Conference Proceedings of the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era of Gravitational Wave Astronomy (January 3 - 7, 2019, Xiamen, China)

We present a seven-minute long $4\pi$-3D simulation of a shell merger event in a non-rotating $18.88\, M_\odot$ supernova progenitor before the onset of gravitational collapse. The key motivation is to capture the large-scale mixing and asymmetries in the wake of the shell merger before collapse using a self-consistent approach. The $4\pi$ geometry is crucial as it allows us to follow the growth and evolution of convective modes on the largest possible scales. We find significant differences between the kinematic, thermodynamic and chemical evolution of the 3D and the 1D model. The 3D model shows vigorous convection leading to more efficient mixing of nuclear species. In the 3D case the entire oxygen shell attains convective Mach numbers of $\mathord{\approx}\, 0.1$, whereas in the 1D model, the convective velocities are much lower and there is negligible overshooting across convective boundaries. In the 3D case, the convective eddies entrain nuclear species from the neon (and carbon) layers into the deeper part of the oxygen burning shell, where they burn and power a violent convection phase with outflows. This is a prototypical model of a convective-reactive system. Due to the strong convection and the resulting efficient mixing, the interface between the neon layer and the silicon-enriched oxygen layer disappears during the evolution, and silicon is mixed far out into merged oxygen/neon shell. Neon entrained inwards by convective downdrafts burns, resulting in lower neon mass in the 3D model compared to the 1D model at time of collapse. In addition, the 3D model develops remarkable large-scale, large-amplitude asymmetries, which may have important implications for the impending gravitational collapse and the subsequent explosion., Comment: 23 pages, 18 figure, Accepted to The ApJ (matches the accepted version)

We present the new code NADA-FLD to solve multi-dimensional neutrino-hydrodynamics in full general relativity (GR) in spherical polar coordinates. The energy-dependent neutrino transport assumes the flux-limited diffusion (FLD) approximation and evolves the neutrino energy densities measured in the frame comoving with the fluid. Operator splitting is used to avoid multi-dimensional coupling of grid cells in implicit integration steps involving matrix inversions. Terms describing lateral diffusion and advection are integrated explicitly using the Allen-Cheng or the Runge-Kutta-Legendre method, which remain stable even in the optically thin regime. We discuss several toy-model problems in one and two dimensions to test the basic functionality and individual components of the transport scheme. We also perform fully dynamic core-collapse supernova (CCSN) simulations in spherical symmetry. For a Newtonian model we find good agreement with the M1 code ALCAR, and for a GR model we reproduce the main effects of GR in CCSNe already found by previous works., Comment: 28 pages, 11 figures; accepted by MNRAS; supplemented by RKL method, resolution tests, and appendix with detailed derivations of FLD flux in response to referee comments

Light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive helium stars that have been evolved including mass loss. These presupernova stars should approximate the results of binary evolution for stars in interacting systems that lose their envelopes close to the time of helium core ignition. Initial helium star masses are in the range 2.5 to 40\,\Msun, which correspond to main sequence masses of about 13 to 90\,\Msun. Common Type Ib and Ic supernovae result from stars whose final masses are approximately 2.5 to 5.6\,\Msun. For heavier stars, a large fraction of collapses lead to black holes, though there is an island of explodability for presupernova masses near 10\,\Msun. The median neutron star mass in binaries is 1.35--1.38\,\Msun \ and the median black hole mass is between 9 and 11\,\Msun. Even though black holes less massive than 5 \Msun\ are rare, they are predicted down to the maximum neutron star mass. There is no empty ``gap'', only a less populated mass range. For standard assumptions regarding the explosions and nucleosynthesis, the models predict light curves that are fainter than the brighter common Type Ib and Ic supernovae. Even with a very liberal, but physically plausible increase in $^{56}$Ni production, the highest energy models are fainter, at peak, than 10$^{42.6}$\,erg\,s$^{-1}$, and very few approach that limit. The median peak luminosity ranges from 10$^{42.0}$ to 10$^{42.3}$\,erg\,s$^{-1}$. Possible alternatives to the standard neutrino-powered and radioactive-illuminated models are explored. Magnetars are a promising alternative. Several other unusual varieties of Type I supernovae at both high and low mass are explored., Comment: 50 pages, 36 figures, 10 tables; submitted to ApJ

Rotation of core-collapse supernovae (SNe) affects the neutrino emission characteristics. By comparing the neutrino properties of three three-dimensional SN simulations of a 15 M_sun progenitor (one non-rotating model and two models rotating at different velocities), we investigate how the neutrino emission varies with the flow dynamics in the SN core depending on the different degrees of rotation. The large-amplitude sinusoidal modulations due to the standing accretion-shock instability (SASI) are weaker in both the rotating models than in the non-rotating case. The SN progenitor rotation reduces the radial velocities and radial component of the kinetic energy associated with convection interior to the proto-neutron star. This effect seems to disfavor the growth of the hemispheric neutrino-emission asymmetries associated with the lepton-emission self-sustained asymmetry (LESA). An investigation of the multipole expansion of the neutrino luminosity and the electron neutrino lepton number flux shows a dominant quadrupolar mode in rotating SN models. Our findings highlight the power of using neutrinos as probes of SN hydrodynamics., Comment: 21 pages, including 17 figures. Characterization of LESA in rotating models expanded; conclusions unchanged. Animated visualizations available at: https://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Walk2018/

Acta physica Polonica / B 51(3), 551 - 559 (2020). doi:10.5506/APhysPolB.51.551, Published by Inst. of Physics, Jagellonian Univ., Cracow

We present a new method for solving the three-dimensional gravitational potential of a density field on the Yin-Yang grid. Our algorithm is based on a multipole decomposition and completely symmetric with respect to the two Yin-Yang grid patches. It is particularly efficient on distributed-memory machines with a large number of compute tasks, because the amount of data being explicitly communicated is minimized. All operations are performed on the original grid without the need for interpolating data onto an auxiliary spherical mesh., 8 pages, 4 figures; two minor additions after refereeing; accepted by ApJ

The material expelled by core-collapse supernova (SN) explosions absorbs X-rays from the central regions. We use SN models based on three-dimensional neutrino-driven explosions to estimate optical depths to the center of the explosion, compare different progenitor models, and investigate the effects of explosion asymmetries. The optical depths below 2 keV for progenitors with a remaining hydrogen envelope are expected to be high during the first century after the explosion due to photoabsorption. A typical optical depth is $100 t_4^{-2} E^{-2}$, where $t_4$ is the time since the explosion in units of 10 000 days (${\sim}$27 years) and $E$ the energy in units of keV. Compton scattering dominates above 50 keV, but the scattering depth is lower and reaches unity already at ${\sim}$1000 days at 1 MeV. The optical depths are approximately an order of magnitude lower for hydrogen-stripped progenitors. The metallicity of the SN ejecta is much higher than in the interstellar medium, which enhances photoabsorption and makes absorption edges stronger. These results are applicable to young SN remnants in general, but we explore the effects on observations of SN 1987A and the compact object in Cas A in detail. For SN 1987A, the absorption is high and the X-ray upper limits of ${\sim}$100 Lsun on a compact object are approximately an order of magnitude less constraining than previous estimates using other absorption models. The details are presented in an accompanying paper. For the central compact object in Cas A, we find no significant effects of our more detailed absorption model on the inferred surface temperature., 21 pages, 7 figures. Accepted for publication in ApJ. Updated to match accepted version; added Section 2.5 on asymmetries and discussion on homologous expansion in preamble of Section 4

Measuring the rotation of core-collapse supernovae (SN) and of their progenitor stars is extremely challenging. Here it is demonstrated that neutrinos may potentially be employed as stellar gyroscopes, if phases of activity by the standing accretion-shock instability (SASI) affect the neutrino emission prior to the onset of the SN explosion. This is shown by comparing the neutrino emission properties of self-consistent, three-dimensional (3D) SN simulations of a 15 M_sun progenitor without rotation as well as slow and fast rotation compatible with observational constraints. The explosion of the fast rotating model gives rise to long-lasting, massive polar accretion downflows with stochastic time-variability, detectable e.g. by the IceCube Neutrino Observatory for any observer direction. While spectrograms of the neutrino event rate of non-rotating SNe feature a well-known sharp peak due to SASI for observers located in the proximity of the SASI plane, the corresponding spectrograms of rotating models show activity over a wide range of frequencies, most notably above 200 Hz for rapid rotation. In addition, the Fourier power spectra of the event rate for rotating models exhibit a SASI peak with lower power than in non-rotating models. The spectra for the rotating models also show secondary peaks at higher frequencies with greater relative heights compared to the main SASI peak than for non-rotating cases. These rotational imprints will be detectable for SNe at 10 kpc or closer., Comment: 10 pages, including 6 figures. Minor changes in the text, matches version accepted for publication in Phys. Rev. D. Animated visualizations available at: https://wwwmpa.mpa-garching.mpg.de/ccsnarchive/data/Walk2018/

We present a new, computationally efficient, energy-integrated approximation for neutrino effects in hot and dense astrophysical environments such as supernova cores and compact binary mergers and their remnants. Our new method, termed ILEAS for Improved Leakage-Equilibration-Absorption Scheme, improves the lepton-number and energy losses of traditional leakage descriptions by a novel prescription of the diffusion time-scale based on a detailed energy integral of the flux-limited diffusion equation. The leakage module is supplemented by a neutrino-equilibration treatment that ensures the proper evolution of the total lepton number and medium plus neutrino energies as well as neutrino-pressure effects in the neutrino-trapping domain. Moreover, we employ a simple and straightforwardly applicable ray-tracing algorithm for including re-absorption of escaping neutrinos especially in the decoupling layer and during the transition to semi-transparent conditions. ILEAS is implemented on a three-dimensional (3D) Cartesian grid with a minimum of free and potentially case-dependent parameters and exploits the basic physics constraints that should be fulfilled in the neutrino-opaque and free-streaming limits. We discuss a suite of tests for stationary and time-dependent proto-neutron star models and post-merger black-hole-torus configurations, for which 3D ILEAS results are demonstrated to agree with energy-dependent 1D and 2D two-moment (M1) neutrino transport on the level of 10--15 percent in basic neutrino properties. This also holds for the radial profiles of the neutrino luminosities and of the electron fraction. Even neutrino absorption maps around torus-like neutrino sources are qualitatively similar without any fine-tuning, confirming that ILEAS can satisfactorily reproduce local losses and re-absorption of neutrinos as found in sophisticated transport calculations., Comment: 39 pages, 19 figures; revised version incl. referee requests; new Sect.3.4 with first NS-NS merger models added; accepted by MNRAS

Neutron stars (NSs) obtain kicks of typically several 100 km/s at birth. The gravitational tug-boat mechanism can explain these kicks as consequences of asymmetric mass ejection during the supernova (SN) explosion. Support for this hydrodynamic explanation is provided by observations of SN remnants with associated NSs, which confirm the prediction that the bulk of the explosion ejecta, in particular chemical elements between silicon and the iron group, are dominantly expelled in the hemisphere opposite to the direction of the NS kick. Here, we present a large set of two- and three-dimensional explosion simulations of electron-capture SNe, considering explosion energies between ~3x10^49 erg and ~1.6x10^50 erg. We find that the fast acceleration of the SN shock in the steep density gradient delimiting the O-Ne-Mg core of the progenitor enables such a rapid expansion of neutrino-heated matter that the growth of neutrino-driven convection freezes out quickly in a high-mode spherical harmonics pattern. Since the corresponding momentum asymmetry of the ejecta is very small and the gravitational acceleration by the fast-expanding ejecta abates rapidly, the NS kick velocities are at most a few km/s. The extremely low core compactness of O-Ne-Mg-core progenitors therefore favors hydrodynamic NS kicks much below the ~160 km/s measured for the Crab pulsar. This suggests either that the Crab Nebula is not the remnant of an electron-capture SN, but of a low-mass iron-core progenitor, or that the Crab pulsar was not accelerated by the gravitational tug-boat mechanism but received its kick by a non-hydrodynamic mechanism such as, e.g., anisotropic neutrino emission., Comment: 23 pages, 9 figures; revised version accounting for referee and reader comments; accepted by ApJ

The remnant of neutron star mergers is dense in neutrinos. By employing inputs from one hydrodynamical simulation of a binary neutron star merger remnant with a black hole of $3\ M_\odot$ in the center, dimensionless spin parameter $0.8$ and an accretion torus of $0.3\ M_\odot$, the neutrino emission properties are investigated as the merger remnant evolves. Initially, the local number density of $\bar{\nu}_e$ is larger than that of $\nu_e$ everywhere above the remnant. Then, as the torus approaches self-regulated equilibrium, the local abundance of neutrinos overcomes that of antineutrinos in a funnel around the polar region. The region where the fast pairwise flavor conversions can occur shrinks accordingly as time evolves. Still, we find that fast flavor conversions do affect most of the neutrino-driven ejecta. Assuming that fast flavor conversions lead to flavor equilibration, a significant enhancement of nuclei with mass numbers $A>130$ is found as well as a change of the lanthanide mass fraction by more than a factor of a thousand. Our findings hint towards a potentially relevant role of neutrino flavor oscillations for the prediction of the kilonova (macronova) lightcurves and motivate further work in this direction., Comment: 16 pages, 12 figures, minor modifications to match the published version

We discuss the equation-of-state dependence of the gravitational-wave signal of neutron-star mergers. For a given binary mass the dominant oscillation frequency of the postmerger remnant scales tightly with neutron star radii of a given mass. This relation means that a measurement of the dominant GW frequency, when combined with information from the inspiral phase, implies a simultaneous mass and radius measurement. Moreover, we derive a procedure by which the detection of two merger events with somewhat different binary masses can be employed for an estimate of the maximum mass of nonrotating neutron stars, the radius of the maximum-mass configuration and the maximum central density of neutron stars. Compared to our method recently described in [7] we here employ a slightly modified procedure.

In the delayed explosion scenario of a core-collapse supernova, the accretion phase shows pronounced convective over-turns and a low-multipole hydrodynamic instability, the so-called standing accretion shock instability (SASI). Neutrino signal variations from the first full-scale three-dimensional core-collapse supernova simulations with sophisticated neutrino transport are presented as well as their detection perspectives in IceCube and Hyper-Kamiokande.

Double neutron star (DNS) systems represent extreme physical objects and the endpoint of an exotic journey of stellar evolution and binary interactions. Large numbers of DNS systems and their mergers are anticipated to be discovered using the Square-Kilometre-Array searching for radio pulsars and high-frequency gravitational wave detectors (LIGO/VIRGO), respectively. Here we discuss all key properties of DNS systems, as well as selection effects, and combine the latest observational data with new theoretical progress on various physical processes with the aim of advancing our knowledge on their formation. We examine key interactions of their progenitor systems and evaluate their accretion history during the high-mass X-ray binary stage, the common envelope phase and the subsequent Case BB mass transfer, and argue that the first-formed NSs have accreted at most $\sim 0.02\;M_{\odot}$. We investigate DNS masses, spins and velocities, and in particular correlations between spin period, orbital period and eccentricity. Numerous Monte Carlo simulations of the second supernova (SN) events are performed to extrapolate pre-SN stellar properties and probe the explosions. All known close-orbit DNS systems are consistent with ultra-stripped exploding stars. Although their resulting NS kicks are often small, we demonstrate a large spread in kick magnitudes which may, in general, depend on the past interaction history of the exploding star and thus correlate with the NS mass. We analyze and discuss NS kick directions based on our SN simulations. Finally, we discuss the terminal evolution of close-orbit DNS systems until they merge and possibly produce a short $\gamma$-ray burst., Comment: 62 pages (emulateapj), 40 figures, 7 tables, published in ApJ. Minor typos fixed, two figures updated and text on ULXs updated. Published version is available here: https://doi.org/10.3847/1538-4357/aa7e89

We present the first self-consistent, three-dimensional (3D) core-collapse supernova simulations performed with the Prometheus-Vertex code for a rotating progenitor star. Besides using the angular momentum of the 15 solar-mass model as obtained in the stellar evolution calculation with an angular frequency of about 0.001 rad/s (spin period of more than 6000 s) at the Si/Si-O interface, we also computed 2D and 3D cases with no rotation and with a ~300 times shorter rotation period and different angular resolutions. In 2D, only the nonrotating and slowly rotating models explode, while rapid rotation prevents an explosion within 500 ms after bounce because of lower radiated neutrino luminosities and mean energies and thus reduced neutrino heating. In contrast, only the fast rotating model develops an explosion in 3D when the Si/Si-O interface collapses through the shock. The explosion becomes possible by the support of a powerful SASI spiral mode, which compensates for the reduced neutrino heating and pushes strong shock expansion in the equatorial plane. Fast rotation in 3D leads to a "two-dimensionalization" of the turbulent energy spectrum (yielding roughly a -3 instead of a -5/3 power-law slope at intermediate wavelengths) with enhanced kinetic energy on the largest spatial scales. We also introduce a generalization of the "universal critical luminosity condition" of Summa et al. (2016) to account for the effects of rotation, and demonstrate its viability for a set of more than 40 core-collapse simulations including 9 and 20 solar-mass progenitors as well as black-hole forming cases of 40 and 75 solar-mass stars to be discussed in forthcoming papers., 24 pages, 19 figures; refereed version with additional section on resolution dependence; accepted by ApJ