We present results from fully relativistic three-dimensional core-collapse supernova simulations of a non-rotating  M 15 star using three different nuclear equations of state (EoSs). From our simulations covering up to ∼350 ms after bounce, we show that the development of the standing accretion shock instability (SASI) differs significantly depending on the stiffness of nuclear EoS. Generally, the SASI activity occurs more vigorously in models with softer EoS. By evaluating the gravitational-wave (GW) emission, we find a new GW signature on top of the previously identified one, in which the typical GW frequency increases with time due to an accumulating accretion to the proto-neutron star (PNS). The newly observed quasi-periodic signal appears in the frequency range from ∼100 to 200 Hz and persists for ∼150 ms before neutrino-driven convection dominates over the SASI. By analyzing the cycle frequency of the SASI sloshing and spiral modes as well as the mass accretion rate to the emission region, we show that the SASI frequency is correlated with the GW frequency. This is because the SASIinduced temporary perturbed mass accretion strikes the PNS surface, leading to the quasi-periodic GW emission. Our results show that the GW signal, which could be a smoking-gun signature of the SASI, is within the detection limits of LIGO, advanced Virgo, and KAGRA for Galactic events.

We present a new multi-dimensional radiation-hydrodynamics code for massive stellar core-collapse in full general relativity (GR). Employing an M1 analytical closure scheme, we solve spectral neutrino transport of the radiation energy and momentum based on a truncated moment formalism. Regarding neutrino opacities, we take into account a baseline set in state-of-the-art simulations, in which inelastic neutrino-electron scattering, thermal neutrino production via pair annihilation, and nucleon-nucleon bremsstrahlung are included. While the Einstein field equations and the spatial advection terms in the radiation-hydrodynamics equations are evolved explicitly, the source terms due to neutrino-matter interactions and energy shift in the radiation moment equations are integrated implicitly by an iteration method. To verify our code, we first perform a series of standard radiation tests with analytical solutions that include the check of gravitational redshift and Doppler shift. A good agreement in these tests supports the reliability of the GR multi-energy neutrino transport scheme. We then conduct several test simulations of core-collapse, bounce, and shock stall of a 15M  star in the Cartesian coordinates and make a detailed comparison with published results. Our code performs quite well to reproduce the results of fullBoltzmann neutrino transport especially before bounce. In the postbounce phase, our code basically performs well, however, there are several differences that are most likely to come from the insufficient spatial resolution in our current 3D-GR models. For clarifying the resolution dependence and extending the code comparison in the late postbounce phase, we discuss that next-generation Exaflopsclass supercomputers are needed at least.

We present results from the first generation of multi-dimensional hydrodynamic core-collapse simulations in full general relativity (GR) that include an approximate treatment of neutrino transport. Using a M1 closure scheme with an analytic variable Eddington factor, we solve the energy-independent set of radiation energy and momentum based on the Thorne's momentum formalism. Our newly developed code is designed to evolve the Einstein field equation together with the GR radiation hydrodynamic equations. We follow the dynamics starting from the onset of gravitational core-collapse of a 15 M ⊙ star, through bounce, up to about 100 ms postbounce in this study. By computing four models that differ according to 1D to 3D and by switching from special relativistic (SR) to GR hydrodynamics, we study how the spacial multidimensionality and GR would affect the dynamics in the early postbounce phase. Our 3D results support the anticipation in previous 1D results that the neutrino luminosity and average neutrino energy of any neutrino flavor in the postbounce phase increase when switching from SR to GR hydrodynamics. This is because the deeper gravitational well of GR produces more compact core structures, and thus hotter neutrino spheres at smaller radii. By analyzing the residency timescale to the neutrino-heating timescale in the gain region, we show that the criterion to initiate neutrino-driven explosions can be most easily satisfied in 3D models, irrespective of SR or GR hydrodynamics. Our results suggest that the combination of GR and 3D hydrodynamics provides the most favorable condition to drive a robust neutrino-driven explosion.

We study properties of gravitational waves (GWs) from rotating core-collapse of a 15M ⊙ star by performing three-dimensional general-relativistic hydrodynamic simulations with an approximate neutrino transport. By parametrically changing the precollapse angular momentum, we focus on the effects of rotation on the GW signatures in the early postbounce evolution. Regarding threeflavor neutrino transport, we solve the energy-averaged set of radiation energy and momentum based on the Thorne's momentum formalism. In addition to the gravitational quadrupole radiation from matter motions, we take into account GWs from anisotropic neutrino emission. With these computations, our results present several supporting evidences for the previous anticipation that non-axisymmetric instabilities play an essential role in determining the postbounce GW signatures.During prompt convection, we find that the waveforms show narrow-band and highly quasi-periodic signals which persist until the end of simulations. We point out that such feature reflects the growth of the one-armed spiral modes. The typical frequency of the quasi-periodic waveforms can be well explained by the propagating acoustic waves between the stalled shock and the rotating protoneutron star surface, which suggests the appearance of the standing-accretion-shock instability.Although the GW signals exhibit strong variability between the two polarizations and different observer directions, they are within the detection limits of next generation detectors such as by KAGRA and Advanced LIGO, if the source with sufficient angular momentum is located in our Galaxy. 95.85.Sz, 97.60.Bw

We present results of three-dimensional (3D), radiation-magnetohydrodynamics (MHD) simulations of core-collapse supernovae in full general relativity (GR) with spectral neutrino transport. In order to study the effects of the progenitor’s rotation and magnetic fields, we compute three models, where the precollapse rotation rate and magnetic fields are included parametrically to a 20 M ⊙ star. While we find no shock revival in our two nonmagnetized models during our simulation times (∼500 ms after bounce), the magnetorotational (MR) driven shock expansion immediately initiates after bounce in our rapidly rotating and strongly magnetized model. We show that the expansion of the MR-driven flows toward the polar directions is predominantly driven by the magnetic pressure, whereas the shock expansion toward the equatorial direction is supported by neutrino heating. Our detailed analysis indicates that the growth of the so-called kink instability may hinder the collimation of jets, resulting in the formation of broader outflows. Furthermore, we find a dipole emission of lepton number, only in the MR explosion model, whose asymmetry is consistent with the explosion morphology. Although it is similar to the lepton number emission self-sustained asymmetry (LESA), our analysis shows that the dipole emission occurs not from the proto–neutron star convection zone but from above the neutrino sphere, indicating that it is not associated with the LESA. We also report several unique neutrino signatures, which are significantly dependent on both the time and the viewing angle, if observed, possibly providing rich information regarding the onset of the MR-driven explosion.

We study the final fate of a very massive star by performing full general relativistic (GR), three-dimensional (3D) simulation with three-flavor multi-energy neutrino transport. Utilizing a 70 solar mass zero metallicity progenitor, we self-consistently follow the radiation-hydrodynamics from the onset of gravitational core-collapse until the second collapse of the proto-neutron star (PNS), leading to black hole (BH) formation. Our results show that the BH formation occurs at a post-bounce time of T pb ∼ 300 ms for the 70 M ⊙ star. This is significantly earlier than those in the literature where lower mass progenitors were employed. At a few ∼ 10 ms before BH formation, we find that the stalled bounce shock is revived by intense neutrino heating from the very hot PNS, which is aided by violent convection behind the shock. In the context of 3D-GR core-collapse modeling with multi-energy neutrino transport, our numerical results present the first evidence to validate a fallback BH formation scenario of the 70M ⊙ star.

Optical spectroscopy and photometry of SN 2006aj have been performed with the Subaru telescope at t 1 days after GRB 060218, the X-ray flash with which it was associated. Strong nebular emission lines with 200 an expansion velocity of km s were detected. The peaked but relatively broad [O i] ll6300, 6363 Ϫ1 v ∼ 7300 suggests the existence of ∼2 of materials in which ∼1.3 is oxygen. The core might be produced by a M M , , mildly asymmetric explosion. The spectra are unique among SNe Ic in (1) the absence of [Ca ii] ll7291, 7324 emission and (2) a strong emission feature at ∼7400 , which requires ∼0.05 of newly synthesized 58 Ni. A M , Such a large amount of stable neutron-rich Ni strongly indicates the formation of a neutron star. The progenitor and the explosion energy are constrained to and ergs, respectively. 51 18 M Շ M Շ 22 M E∼ (1-3) # 10

We present an overview of two-dimensional (2D) core-collapse supernova simulations employing 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 10.8 M ⊙ to 75.0 M ⊙ . 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 (1D) studies, our results confirm that the compactness parameter ξ that characterizes the structure of the progenitors is also a key in 2D to diagnose the properties of neutrinodriven 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.