Two‐Dimensional Multiangle, Multigroup Neutrino Radiation‐Hydrodynamic Simulations of Postbounce Supernova Cores

Abstract

We perform axisymmetric (2D) multi-angle, multi-group neutrino\nradiation-hydrodynamic calculations of the postbounce phase of core-collapse\nsupernovae using a genuinely 2D discrete-ordinate (S_n) method. We follow the\nlong-term postbounce evolution of the cores of one nonrotating and one\nrapidly-rotating 20-solar-mass stellar model for ~400 milliseconds from 160 ms\nto ~550 ms after bounce. We present a multi-D analysis of the multi-angle\nneutrino radiation fields and compare in detail with counterpart simulations\ncarried out in the 2D multi-group flux-limited diffusion (MGFLD) approximation\nto neutrino transport. We find that 2D multi-angle transport is superior in\ncapturing the global and local radiation-field variations associated with\nrotation-induced and SASI-induced aspherical hydrodynamic configurations. In\nthe rotating model, multi-angle transport predicts much larger asymptotic\nneutrino flux asymmetries with pole to equator ratios of up to ~2.5, while\nMGFLD tends to sphericize the radiation fields already in the optically\nsemi-transparent postshock regions. Along the poles, the multi-angle\ncalculation predicts a dramatic enhancement of the neutrino heating by up to a\nfactor of 3, which alters the postbounce evolution and results in greater polar\nshock radii and an earlier onset of the initially rotationally weakened SASI.\nIn the nonrotating model, differences between multi-angle and MGFLD\ncalculations remain small at early times when the postshock region does not\ndepart significantly from spherical symmetry. At later times, however, the\ngrowing SASI leads to large-scale asymmetries and the multi-angle calculation\npredicts up to 30% higher average integral neutrino energy deposition rates\nthan MGFLD.\n