The relevance of the standing accretion shock instability (SASI) compared to neutrino-driven convection in three-dimensional (3D) supernova-core environments is still highly controversial. Studying a 27 M ⊙ progenitor, we demonstrate, for the first time, that violent SASI activity can develop in 3D simulations with detailed neutrino transport despite the presence of convection. This result was obtained with the Prometheus-Vertex code with the same sophisticated neutrino treatment so far used only in 1D and 2D models. While buoyant plumes initially determine the nonradial mass motions in the postshock layer, bipolar shock sloshing with growing amplitude sets in during a phase of shock retraction and turns into a violent spiral mode whose growth is only quenched when the infall of the Si/SiO interface leads to strong shock expansion in response to a dramatic decrease of the mass accretion rate. In the phase of large-amplitude SASI sloshing and spiral motions, the postshock layer exhibits nonradial deformation dominated by the lowest-order spherical harmonics (ℓ = 1, m = 0, ±1) in distinct contrast to the higher multipole structures associated with neutrino-driven convection. We find that the SASI amplitudes, shock asymmetry, and nonradial kinetic energy in 3D can exceed those of the corresponding 2D case during extended periods of the evolution. We also perform parametrized 3D simulations of a 25 M ⊙ progenitor, using a simplified, gray neutrino transport scheme, an axis-free Yin-Yang grid, and different amplitudes of random seed perturbations. They confirm the importance of the SASI for another progenitor, its independence of the choice of spherical grid, and its preferred growth for fast accretion flows connected to small shock radii and compact proto-neutron stars as previously found in 2D setups.

We present three-dimensional hydrodynamic simulations of the evolution of core-collapse supernovae (SN) from blast-wave initiation by the neutrino-driven mechanism to shock breakout from the stellar surface, using an axis-free Yin-Yang grid and considering two 15 M red supergiants (RSG) and two blue supergiants (BSG) of 15 M and 20 M . We demonstrate that the metal-rich ejecta in homologous expansion still carry fingerprints of asymmetries at the beginning of the explosion, but the final metal distribution is massively affected by the detailed progenitor structure. The most extended and fastest metal fingers and clumps are correlated with the biggest and fastest-rising plumes of neutrino-heated matter, because these plumes most effectively seed the growth of RayleighTaylor (RT) instabilities at the C+O/He and He/H composition-shell interfaces after the passage of the SN shock. The extent of radial mixing, global asymmetry of the metal-rich ejecta, RT-induced fragmentation of initial plumes to smaller-scale fingers, and maximum Ni and minimum H velocities depend not only on the initial asphericity and explosion energy (which determine the shock and initial Ni velocities), but also on the density profiles and widths of C+O core and He shell and on the density gradient at the He/H transition, which leads to unsteady shock propagation and the formation of reverse shocks. Both RSG explosions retain a large global metal asymmetry with pronounced clumpiness and substructure, deep penetration of Ni fingers into the H-envelope (with maximum velocities of 4000-5000 km s −1 for an explosion energy around 1.5 bethe) and efficient inward H-mixing. While the 15 M BSG shares these properties (maximum Ni speeds up to ∼3500 km s −1 ), the 20 M BSG develops a much more roundish geometry without pronounced metal fingers (maximum Ni velocities only ∼2200 km s −1 ) because of reverse-shock deceleration and insufficient time for strong RT growth and fragmentation at the He/H interface.

We present three-dimensional (3D) simulations of supernova explosions of nonrotating stars, triggered by the delayed neutrinoheating mechanism with a suitable choice of the core-neutrino luminosity. Our results show that asymmetric mass ejection caused by hydrodynamic instabilities can accelerate the neutron star (NS) up to recoil velocities of more than 700 km s −1 by the "gravitational tug-boat mechanism", which is sufficient to explain most observed pulsar space velocities. The associated NS spin periods for our nonrotating progenitors are about 100 ms to 8000 ms without any obvious correlation between spin and kick magnitudes or directions. This suggests that faster spins and a possible spin-kick alignment might require angular momentum in the progenitor core prior to collapse. Our simulations for the first time demonstrate a clear correlation between the size of the NS kick and anisotropic production and distribution of heavy elements created by explosive burning behind the shock. In the case of large pulsar kicks, the explosion is significantly stronger opposite to the kick vector. Therefore the bulk of the explosively fused iron-group elements, in particular nickel, are ejected mostly in large clumps against the kick direction. This contrasts with the case of low recoil velocity, where the nickelrich lumps are more isotropically distributed. Explosively produced intermediate-mass nuclei heavier than 28 Si (like 40 Ca and 44 Ti) also exhibit significant enhancement in the hemisphere opposite to the direction of fast NS motion, while the distribution of 12 C, 16 O, and 20 Ne is not affected, and that of 24 Mg only marginally. Mapping the spatial distribution of the heavy elements in supernova remnants with identified pulsar motion may offer an important diagnostic test of the kick mechanism. Unlike kick scenarios based on anisotropic neutrino emission, our hydrodynamical acceleration model predicts enhanced ejection of iron-group elements and of their nuclear precursors in the opposite direction to the NS recoil.

The spatial and velocity distributions of nuclear species synthesized in the innermost regions of core-collapse supernovae (SNe) can yield important clues about explosion asymmetries and the operation of the still disputed explosion mechanism. Recent observations of radioactive 44 Ti with high-energy satellite telescopes (NuSTAR, INTEGRAL) have measured gamma-ray line details, which provide direct evidence of large-scale explosion asymmetries in Supernova 1987A, and in Cassiopeia A (Cas A) even by mapping of the spatial brightness distribution (NuSTAR). Here, we discuss a three-dimensional (3D) simulation of a neutrino-driven explosion, using a parametrized neutrino engine, whose 44 Ti distribution is mostly concentrated in one hemisphere pointing opposite to the neutron-star (NS) kick velocity. Both exhibit intriguing resemblance to the observed morphology of the Cas A remnant, although neither progenitor nor explosion were fine-tuned for a perfect match. Our results demonstrate that the asymmetries observed in this remnant can, in principle, be accounted for by a neutrino-driven explosion, and that the high 44 Ti abundance in Cas A may be explained without invoking rapid rotation or a jet-driven explosion, because neutrino-driven explosions genericly eject large amounts of highentropy matter. The recoil acceleration of the NS is connected to mass-ejection asymmetries and is opposite to the direction of the stronger explosion, fully compatible with the gravitational tug-boat mechanism. Our results also imply that Cas A and SN 1987A could possess similarly "one-sided" Ti and Fe asymmetries, with the difference that Cas A is viewed from a direction with large inclination angle to the NS motion, whereas the NS in SN 1987A should have a dominant velocity component pointing toward us.

Using three-dimensional (3D) simulations of neutrino-powered supernova explosions we show that the hydrodynamical kick scenario proposed by Scheck et al. on the basis of two-dimensional (2D) models can yield large neutron star (NS) recoil velocities also in 3D. Although the shock stays relatively spherical, standing accretion-shock and convective instabilities lead to a globally asymmetric mass and energy distribution in the postshock layer. An anisotropic momentum distribution of the ejecta is built up only after the explosion sets in. Total momentum conservation implies the acceleration of the NS on a timescale of 1-3 seconds, mediated mainly by long-lasting, asymmetric accretion downdrafts and the anisotropic gravitational pull of large inhomogeneities in the ejecta. In a limited set of 15 M ⊙ models with an explosion energy of about 10 51 erg this stochastic mechanism is found to produce kicks from <100 km s −1 to 500 km s −1 , and 1000 km s −1 seem possible. Strong rotational flows around the accreting NS do not develop in our collapsing, non-rotating progenitors. The NS spins therefore remain low with estimated periods of ∼500-1000 ms and no alignment with the kicks.

Time-dependent and direction-dependent neutrino and gravitational-wave (GW) signatures are presented for a set of three-dimensional (3D) hydrodynamic models of parametrized, neutrino-driven supernova explosions of non-rotating 15 and 20 M stars. We employed an approximate treatment of neutrino transport based on a gray spectral description and a ray-by-ray treatment of multi-dimensional effects. Owing to the excision of the high-density core of the proto-neutron star (PNS) and the use of an axis-free (Yin-Yang) overset grid, the models can be followed from the post-bounce accretion phase through the onset of the explosion into more than one second of the early cooling evolution of the PNS without imposing any symmetry restrictions and covering a full sphere. Gravitational waves and neutrino emission exhibit the generic time-dependent features already known from 2D (axi-symmetric) models. Violent non-radial hydrodynamic mass motions in the accretion layer and their interaction with the outer layers of the proto-neutron star together with anisotropic neutrino emission give rise to a GW signal with an amplitude of ∼5−20 cm in the frequency range of 100−500 Hz. The GW emission from mass motions usually reaches a maximum before the explosion sets in. After the onset of the explosion the GW signal exhibits a low-frequency modulation, in some cases describing a quasi-monotonic growth, associated with the non-spherical expansion of the explosion shock wave and the large-scale anisotropy of the escaping neutrino flow. Variations of the mass-quadrupole moment caused by convective activity inside the nascent neutron star add a high-frequency component to the GW signal during the post-explosion phase. The GW signals exhibit strong variability between the two polarizations, different explosion simulations and different observer directions, and besides common basic features do not possess any template character. The neutrino emission properties (fluxes and effective spectral temperatures) show fluctuations over the neutron star surface on spatial and temporal scales that reflect the different types of non-spherical mass motions in the supernova core, i.e., post-shock overturn flows and proto-neutron star convection. However, because very prominent, quasi-periodic sloshing motions of the shock caused by the standing accretion-shock instability are absent and the emission from different surface areas facing an observer adds up incoherently, the modulation amplitudes of the measurable neutrino luminosities and mean energies are significantly lower than predicted by 2D simulations.

ABSTRACT We present 3D full-sphere supernova simulations of non-rotating low-mass (∼9 M⊙) 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 × 1050 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 second 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 $\mathord {\lesssim }\, 5\, \mathord {\times }\, 10^{-3}$ M⊙ have no significant effects on the neutron star (NS) masses and kicks. The anisotropic fallback carries considerable angular momentum, however, and determines the spin of the newly born NS. The LMCCSN model with less second dredge-up results in a hydrodynamic and neutrino-induced NS kick of &gt;40 km s−1 and a NS spin period of ∼30 ms, both not largely different from those of the Crab pulsar at birth.

Context. The well-observed and well-studied type IIP Supernova 1987A (SN 1987A), produced by the explosion of a blue supergiant in the Large Magellanic Cloud, is a touchstone for the evolution of massive stars, the simulation of neutrino-driven explosions, and the modeling of light curves and spectra. Aims. In the framework of the neutrino-driven explosion mechanism, we study the dependence of explosion properties on the structure of different blue supergiant progenitors and compare the corresponding light curves with observations of SN 1987A. Methods. Three-dimensional (3D) simulations of neutrino-driven explosions are performed with the explicit, finite-volume, Eulerian, multifluid hydrodynamics code Prometheus, using of four available presupernova models as initial data. At a stage of almost homologous expansion, the hydrodynamical and composition variables of the 3D models are mapped to a spherically symmetric configuration, and the simulations are continued with the implicit, Lagrangian radiation-hydrodynamics code Crab to follow the blast-wave evolution into the SN outburst. Results. All of our 3D neutrino-driven explosion models, with explosion energies compatible with SN 1987A, produce 56 Ni in rough agreement with the amount deduced from fitting the radioactively powered light-curve tail. Two of our models (based on the same progenitor) yield maximum velocities of around 3000 km s −1 for the bulk of ejected 56 Ni, consistent with observational data. In all of our models inward mixing of hydrogen during the 3D evolution leads to minimum velocities of hydrogen-rich matter below 100 km s −1 , which is in good agreement with spectral observations. However, the explosion of only one of the considered progenitors reproduces the shape of the broad light curve maximum of SN 1987A fairly well. Conclusions. The considered presupernova models, 3D explosion simulations, and light-curve calculations can explain the basic observational features of SN 1987A, except for those connected to the presupernova structure of the outer stellar layers. All progenitors have presupernova radii that are too large to reproduce the narrow initial luminosity peak, and the structure of their outer layers is not suitable to match the observed light curve during the first 30-40 days. Only one stellar model has a structure of the helium core and the He/H composition interface that enables sufficient outward mixing of 56 Ni and inward mixing of hydrogen to produce a good match of the dome-like shape of the observed light-curve maximum, but this model falls short of the helium-core mass of 6 M inferred from the absolute luminosity of the presupernova star. The lack of an adequate presupernova model for the well-studied SN 1987A is a real and pressing challenge for the theory of the evolution of massive stars.