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Supernova Neutrinos and a New Algorithm for Neutrino Transport

We have developed a new implicit, multi–group, time–dependent, spherical neutrino transport algorithm based on the Feautrier variables, the tangent–ray method, and accelerated Λ iteration. The code achieves high angular resolution, is conceptually equivalent to a Boltzmann solver (without redshifts), and solves the transport equation exactly at all optical depths. We summarize and review the neutrino physics of stellar collapse and supernovae and our formulation of the relevant microphysics. In addition, we derive various useful expressions for neutrino source strengths, including those for nucleon–nucleon bremsstrahlung. With this code, we study the character of protoneutron star atmospheres for snapshot post–bounce models, with particular emphasis on their spectra, Eddington factors and angular distributions, phase–space occupancies, and neutrino–matter heating rates. Concerning the latter, we explore the influence of final–state electron blocking, stimulated absorption, velocity terms in the transport equation, neutrino–nucleon scattering asymmetry, and weak magnetism and recoil effects. We also investigate the physical determinants of the νμ spectra that emerge from supernova cores and the neutrino heating rates in post–explosion protoneutron star winds. These studies are in preparation for new calculations of spherically symmetric core–collapse supernovae, protoneutron star winds, and neutrino signals, but are also meant to establish a high–accuracy benchmark for future studies of the neutrino atmospheres of evolving protoneutron stars. Subject headings: supernovae, neutrinos, radiative transfer, atmospheres, spectra Department of Astronomy and Steward Observatory, The University of Arizona, Tucson, AZ 85721 Lawrence Livermore National Laboratory, Livermore, CA 94551 Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 Department of Physics, The University of Arizona, Tucson, AZ 85721