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.

Abstract.We have performed two-dimensional simulations of core collapse supernovae that encompass shock revival by neutrino heating, neutrino-driven convection, explosive nucleosynthesis, the growth of Rayleigh-Taylor instabilities, and the propagation of newly formed metal clumps through the exploding star. A simulation of a type II explosion in a 15 M blue supergiant progenitor is presented, that confirms our earlier type II models and extends their validity to times as late as 5.5 hours after core bounce. We also study a type Ib-like explosion, by simply removing the hydrogen envelope of the progenitor model. This allows for a first comparison of type II and type Ib evolution. We present evidence that the hydrodynamics of core collapse supernovae beyond shock revival differs markedly from the results of simulations that have followed the Rayleigh-Taylor mixing starting from ad hoc energy deposition schemes to initiate the explosion. We find iron group elements to be synthesized in an anisotropic, dense, low-entropy shell that expands with velocities of ∼17 000 km s −1 shortly after shock revival. The growth of Rayleigh-Taylor instabilities at the Si/O and (C+O)/He composition interfaces of the progenitor, seeded by the flow-structures resulting from neutrino-driven convection, leads to a fragmentation of this shell into metal-rich "clumps". This fragmentation starts already ∼20 s after core bounce and is complete within the first few minutes of the explosion. During this time the clumps are slowed down by drag, and by the positive pressure gradient in the unstable layers. However, at t ≈ 300 s they decouple from the flow and start to propagate ballistically and subsonically through the He core, with the maximum velocities of metals remaining constant at ∼3500−5500 km s −1 . This early "clump decoupling" leads to significantly higher 56 Ni velocities at t = 300 s than in one-dimensional models of the explosion, demonstrating that multi-dimensional effects which are at work within the first minutes, and which have been neglected in previous studies (especially in those which dealt with the mixing in type II supernovae), are crucial. Despite comparably high initial maximum nickel velocities in both our type II and our type Ib-like model, we find that there are large differences in the final maximum nickel velocities between both cases. In the "type Ib" model the maximum velocities of metals remain frozen in at ∼3500−5500 km s −1 for t ≥ 300 s, while in the type II model they drop significantly for t > 1500 s. In the latter case, the massive hydrogen envelope of the progenitor forces the supernova shock to slow down strongly, leaving behind a reverse shock and a dense helium shell (or "wall") below the He/H interface. After penetrating into this dense material the metal-rich clumps possess supersonic speeds, before they are slowed down by drag forces to ∼1200 km s −1 at a time of 20 000 s post-bounce. While, due to this deceleration, the maximum velocities of iron-group elements in SN 1987 A cannot be reproduced ...

Abstract. We present the first general relativistic hydrodynamic models of the launch and evolution of relativistic jets and winds, driven by thermal energy deposition, possibly due to neutrino-antineutrino annihilation, in the close vicinity of black hole-accretion torus systems. The latter are considered to be the remnants of compact object mergers. Our two-dimensional simulations establish the link between models of such mergers and future observations of short gamma-ray bursts by the SWIFT satellite. They show that ultrarelativistic outflow with maximum terminal Lorentz factors around 1000 develops for polar energy deposition rates above some 10 48 erg s −1 per steradian, provided the merger environment has a sufficiently low baryon density. By the interaction with the dense accretion torus the ultrarelativistic outflow with Lorentz factors Γ above 100 is collimated into a sharp-edged cone that is embedded laterally by a wind with steeply declining Lorentz factor. The typical semi-opening angles of the Γ > 100 cone are 5 • −10 • , corresponding to about 0.4−1.5% of the hemisphere and apparent isotropized energies (kinetic plus internal) up to ≈10 51 erg although at most 10−30% of the deposited energy is transferred to the outflow with Γ > 100. The viability of post-merger black hole-torus systems as engines of short, hard gamma-ray bursts is therefore confirmed. The annihilation of neutrino-antineutrino pairs radiated from the hot accretion torus appears as a suitable energy source for powerful axial outflow even if only ≈10 49 erg are deposited within a cone of 45 • half-opening angle around the system axis. Although the torus lifetimes are expected to be only between some 0.01 s and several 0.1 s, our models can explain the durations of all observed short gamma-ray bursts, because different propagation velocities of the front and rear ends will lead to a radial stretching of the ultrarelativistic fireball before transparency is reached. The ultrarelativistic flow reveals a highly non-uniform structure caused by the action of Kelvin-Helmholtz instabilities that originate at the fireball-torus interface. Large radial variations of the baryon density (up to several orders of magnitude) are uncorrelated with moderate variations of the Lorentz factor (factors of a few) and fluctuations of the gently declining radiation-dominated pressure. In the angular direction the Lorentz factor reveals a nearly flat plateau-like maximum with values of several hundreds, that can be located up to 7 • off the symmetry axis, and a steep decrease to less than 10 for polar angles larger than 15 • −20 • . Lateral expansion of the ultrarelativistic core of the flow is prevented by a subsonic velocity component of about 0.05c towards the symmetry axis, whereas the moderately relativistic wings show a subsonic sideways inflation with less than 0.07c (measured in the frame comoving with the radial flow).

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Context. We investigate the deposition of energy and momentum due to the annihilation of neutrinos (ν) and antineutrinos (ν) in the vicinity of steady, axisymmetric accretion tori around stellar-mass black holes (BHs). This process is widely considered as an energy source for driving ultrarelativistic outflows with the potential to produce gamma-ray bursts. Aims. We analyze the influence of general relativistic (GR) effects in combination with different neutrinosphere properties on the νν-annihilation efficiency and spatial distribution of the energy deposition rate. Methods. Assuming axial symmetry, we numerically compute the annihilation rate 4-vector. For this purpose, we construct the local neutrino distribution by ray-tracing neutrino trajectories in a Kerr space-time using null geodesics. We vary the value of the dimensionless specific angular momentum a of the central BH, which provides the gravitational field in our models. We also study different shapes of the neutrinospheres, spheres, thin disks, and thick accretion tori, whose structure ranges from idealized tori to equilibrium non-selfgravitating matter distributions. Furthermore, we compute Newtonian models where the influence of the gravitational field on the annihilation process is neglected. Results. Compared to Newtonian calculations, GR effects increase the total annihilation rate measured by an observer at infinity by a factor of two when the neutrinosphere is a thin disk, but the increase is only ≈25% for toroidal and spherical neutrinospheres. Comparing cases with similar luminosities, thin disk models yield the highest energy deposition rates by νν-annihilation, and spherical neutrinospheres the lowest ones, independently of whether GR effects are included. Increasing a from 0 to 1 enhances the energy deposition rate measured by an observer at infinity by roughly a factor of 2 due to the change of the inner radius of the neutrinosphere. General relativity and rotation cause important differences in the spatial distribution of the energy deposition rate by νν-annihilation.Key words. gamma rays: bursts -neutrinos -accretion, accretion disks -relativity -black hole physics -stars: neutron IntroductionIt is widely believed that systems powering gamma-ray bursts (GRB) could be newborn, stellar-mass black holes (BHs) accreting matter at hyper-critical rates (up to several solar masses per second) from a surrounding accretion disk with a mass of some hundredth of a solar mass up to possibly a solar mass (see, e.g., Piran 2005). These central engines may form in a "collapsar" event where the core of a massive, rotating Wolf-Rayet star collapses to a BH and the accretion of the stellar envelope may eventually lead to a GRB-supernova event with relativistic mass ejection along the rotation axis (Woosley 1993;MacFadyen & Woosley 1999;Aloy et al. 2000). Accreting BHs may also be the remnants of mergers of two compact objects in close binaries (Eichler et al. 1989;Mochkovitch et al. 1993). In the first scenario the system is embedded in the enve...