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The next Galactic supernova is expected to bring great opportunities for the direct detection of gravitational waves (GW), full flavour neutrinos, and multiwavelength photons. To maximize the science return from such a rare event, it is essential to have established classes of possible situations and preparations for appropriate observations. To this end, we use a long-term numerical simulation of the core-collapse supernova (CCSN) of a 17 M☉ red supergiant progenitor to self-consistently model the multimessenger signals expected in GW, neutrino, and electromagnetic messengers. This supernova model takes into account the formation and evolution of a protoneutron star, neutrino-matter interaction, and neutrino transport, all within a two-dimensional shock hydrodynamics simulation. With this, we separately discuss three situations: (i) a CCSN at the Galactic Center, (ii) an extremely nearby CCSN within hundreds of parsecs, and (iii) a CCSN in nearby galaxies within several Mpc. These distance regimes necessitate different strategies for synergistic observations. In a Galactic CCSN, neutrinos provide strategic timing and pointing information. We explore how these in turn deliver an improvement in the sensitivity of GW analyses and help to guarantee observations of early electromagnetic signals. To facilitate the detection of multimessenger signals of CCSNe in extremely nearby and extragalactic distances, we compile a list of nearby red supergiant candidates and a list of nearby galaxies with their expected CCSN rates. By exploring the sequential multimessenger signals of a nearby CCSN, we discuss preparations for maximizing successful studies of such an unprecedented stirring event. [ABSTRACT FROM AUTHOR]

We present an overview of two-dimensional (2D) core-collapse supernova simulations employing a neutrino transport scheme by the isotropic diffusion source approximation. We study 101 solar-metallicity, 247 ultra metal-poor, and 30 zero-metal progenitors covering zero-age main sequence mass from 10.8M⊙ to 75.0M⊙. Using the 378 progenitors in total, we systematically investigate how the differences in the structures of these multiple progenitors impact the hydrodynamics evolution. By following a long-term evolution over 1.0 s after bounce, most of the computed models exhibit neutrino-driven revival of the stalled bounce shock at ~200-800 ms postbounce, leading to the possibility of explosion. Pushing the boundaries of expectations in previous one-dimensional studies, our results confirm that the compactness parameter ξ that characterizes the structure of the progenitors is also a key in 2D to diagnosing the properties of neutrino-driven explosions. Models with high ξ undergo high ram pressure from the accreting matter onto the stalled shock, which affects the subsequent evolution of the shock expansion and the mass of the protoneutron star under the influence of neutrino-driven convection and the standing accretion-shock instability. We show that the accretion luminosity becomes higher for models with high ξ, which makes the growth rate of the diagnostic explosion energy higher and the synthesized nickel mass bigger. We find that these explosion characteristics tend to show a monotonic increase as a function of the compactness parameter ξ. [ABSTRACT FROM AUTHOR]

We suggest the future detection of neutrinos from a Galactic core-collapse supernova can be used to infer the progenitor’s inner mass density structure. We present the results from 20 axisymmetric core-collapse supernova simulations performed with progenitors spanning initial masses in the range 11–, and focus on their connections to the progenitor compactness. The compactness is a measure of the mass density profile of the progenitor core and recent investigations have suggested its salient connections to the outcomes of core collapse. Our simulations confirm a correlation between the neutrinos emitted during the accretion phase and the progenitor’s compactness, and that the ratio of observed neutrino events during the first hundreds of milliseconds provides a promising handle on the progenitor’s inner structure. Neutrino flavor mixing during the accretion phase remains a large source of uncertainty. [ABSTRACT FROM AUTHOR]

We revisit the diffuse supernova neutrino background in light of recent systematic studies of stellar core collapse that reveal the quantitative impacts of the progenitor conditions on the collapse process. In general, the dependence of the core-collapse neutrino emission on the progenitor is not monotonic in progenitor initial mass, but we show that it can, at first order, be characterized by the core compactness. For the first time, we incorporate the detailed variations in the neutrino emission over the entire mass range 8-100M☉, based on (i) a long-term simulation of the core collapse of an 8.8M☉ ONeMg core progenitor, (ii) over 100 simulations of iron core collapse to neutron stars, and (iii) half a dozen simulations of core collapse to black holes (the 'failed channel'). The fraction of massive stars that undergo the failed channel remains uncertain, but in view of recent simulations which reveal high compactness to be conducive to collapse to black holes, we characterize the failed fraction by considering a threshold compactness above which massive stars collapse to black holes and below which the final remnant is a neutron star.We predict that future detections of the diffuse supernova neutrino background may have the power to reveal this threshold compactness, if its value is relatively small as suggested by interpretations of several recent astronomical observations [ABSTRACT FROM AUTHOR]

We propose to employ the circular polarization of gravitational waves emitted by core-collapse supernovae as an unequivocal indication of rapid rotation deep in their cores just prior to collapse. It has been demonstrated by three dimensional simulations that nonaxisymmetric accretion flows may develop spontaneously via hydrodynamical instabilities in the postbounce cores. It is not surprising, then, that the gravitational waves emitted by such fluid motions are circularly polarized. We show, in this Letter, that a network of the second generation detectors of gravitational waves worldwide may be able to detect such polarizations up to the opposite side of the Galaxy as long as the rotation period of the core is shorter than a few seconds prior to collapse. [ABSTRACT FROM AUTHOR]

We perform two- (2D) and three-dimensional (3D) hydrodynamics simulations of convective oxygen-shell burning that takes place deep inside a massive progenitor star of a core-collapse supernova. Using a one-dimensional (1D) stellar evolution code, we first calculate the evolution of massive stars with an initial mass of 9–40 M⊙. Four different overshoot parameters are applied, and a CO-core mass trend similar to previous works is obtained in the 1D models. Selecting eleven 1D models that have a coexisting silicon and oxygen layer, we perform 2D hydrodynamics simulations of the evolution for ∼100 s until the onset of core collapse. We find that convection with large-scale eddies and the turbulent Mach number of ∼0.1 is obtained in the models having a Si/O layer with a scale of 108 cm, whereas most models that have an extended O/Si layer up to a few ×109 cm exhibit lower turbulent velocity. Our results indicate that the supernova progenitors that possess a thick Si/O layer could provide the preferred condition for perturbation-aided explosions. We perform the 3D simulation of a 25 M⊙ model, which exhibits large-scale convection in the 2D models. The 3D model develops large-scale (ℓ = 2) convection similar to the 2D model; however, the turbulent velocity is lower. By estimating the neutrino emission properties of the 3D model, we point out that a time modulation of the event rates, if observed in KamLAND and Hyper-Kamiokande, could provide important information about structural changes in the presupernova convective layer. [ABSTRACT FROM AUTHOR]

The isotope 98Tc decays to 98Ru with a half-life of 4.2×106 yr and could have been present in the early Solar System. In this Letter, we report on the first calculations of the production of 98Tc by neutrino-induced reactions in core-collapse supernovae (the ν process). Our predicted 98Tc abundance at the time of solar system formation is not much lower than the current measured upper limit raising the possibility for its detection in the not too distant future. We show that, if the initial abundance were to be precisely measured, the 98Tc nuclear cosmochronometer could be used to evaluate a much more precise value of the duration time from the last core-collapse supernova to the formation of the solar system. Moreover, a unique and novel feature of the 98Tc ν-process nucleosynthesis is the large contribution (~20%) from charged current reactions with electron antineutrinos. This means that 98Tc becomes a unique new ν-process probe of the temperature of the electron antineutrinos. [ABSTRACT FROM AUTHOR]

We investigate a progenitor mass distribution of core-collapse supernova remnants (CCSNRs) in our Galaxy and Large and Small Magellanic Clouds for the first time. We count the number of CCSNRs in three mass ranges divided by the zero-age main-sequence (ZAMS) mass, MZAMS; A: MZAMS < 15 M⊙, B: 15 M⊙ < MZAMS < 22.5 M⊙, C: MZAMS > 22.5 M⊙. A simple compilation of progenitor masses in the literature yields a progenitor mass distribution of fA : fB : fC = 0.27:0.27:0.46, where f is the number fraction of the progenitors. The distribution is inconsistent with any standard initial mass functions (IMFs). We notice, however, that previous mass estimates are subject to large systematic uncertainties because most of the relative abundances (X/Si) are not good probes for the progenitor masses. Instead, we rely only on the Fe/Si ratio, which is sensitive to the CO core mass (MCOcore) and MZAMS. Comparing Fe/Si ratios in SN remnants in the literature with the newest theoretical model, we estimate 33 MCOcore and MZAMS, leading to a revised progenitor mass distribution of fA : fB : fC = 0.47:0.32:0.21. This is consistent with the standard Salpeter IMF. However, the relation between MCOcore and MZAMS could be affected by binary evolution, which is not taken into account in this study and should be considered in future work to derive a better progenitor mass distribution estimate. [ABSTRACT FROM AUTHOR]

The birth properties of neutron stars (NSs) yield important information about the still-debated physical processes that trigger the explosion as well as on intrinsic neutron-star physics. These properties include the high space velocities of young neutron stars with average values of several 100 km s−1, with an underlying “kick” mechanism that is not fully clarified. There are two competing possibilities that could accelerate NSs during their birth: anisotropic ejection of either stellar debris or neutrinos. Here we present new evidence from X-ray measurements that chemical elements between silicon and calcium in six young gaseous supernova remnants are preferentially expelled opposite to the direction of neutron star motion. There is no correlation between the kick velocities and magnetic field strengths of these neutron stars. Our results support a hydrodynamic origin of neutron-star kicks connected to asymmetric explosive mass ejection, and they conflict with neutron-star acceleration scenarios that invoke anisotropic neutrino emission caused by particle and nuclear physics in combination with very strong neutron-star magnetic fields. [ABSTRACT FROM AUTHOR]

The accurate description of neutrino opacities is central to both the core-collapse supernova (CCSN) phenomenon and the validity of the explosion mechanism itself. In this work, we study in a systematic fashion the role of a variety of well-selected neutrino opacities in CCSN simulations where the multi-energy, three-flavor neutrino transport is solved using the isotropic diffusion source approximation (IDSA) scheme. To verify our code, we first present results from one-dimensional (1D) simulations following the core collapse, bounce, and ∼250 ms postbounce of a star using a standard set of neutrino opacities by Bruenn. A detailed comparison with published results supports the reliability of our three-flavor IDSA scheme using the standard opacity set. We then investigate in 1D simulations how individual opacity updates lead to differences with the baseline run with the standard opacity set. Through detailed comparisons with previous work, we check the validity of our implementation of each update in a step-by-step manner. Individual neutrino opacities with the largest impact on the overall evolution in 1D simulations are selected for systematic comparisons in our two-dimensional (2D) simulations. Special attention is given to the criterion of explodability in the 2D models. We discuss the implications of these results as well as its limitations and the requirements for future, more elaborate CCSN modeling. [ABSTRACT FROM AUTHOR]