Late-Time Convection in the Collapse of a 23 Solar Mass Star

The results of a 3-dimensional SNSPH simulation of the core collapse of a 23M⊙ star are presented. This simulation did not launch an explosion until over 600ms after collapse, allowing an ideal opportunity to study the evolution and structure of the convection below the accretion shock to late times. This late-time convection allows us to study several of the recent claims in the literature about the role of convection: is it dominated by an l = 1 mode driven by vorticalacoustic (or other) instability, does it produce strong neutron star kicks, and, finally, is it the key to a new explosion mechanism? The convective region buffets the neutron star, imparting a 150 − 200 km s kick. Because the l = 1 mode does not dominate the convection, the neutron star does not achieve large (> 450 km s) velocities. Finally, the neutron star in this simulation moves, but does not develop strong oscillations, the energy source for a recently proposed supernova engine. We discuss the implications these results have on supernovae, hypernovae (and gamma-ray bursts), and stellar-massed black holes. Subject headings: Gamma Rays: Bursts, Nucleosynthesis, Stars: Supernovae: General