Monte Carlo simulations of neutrino transport in type II supernovae

Based on a hydrodynamical model of stellar collapse spectra and luminosities of neutrinos of various flavors are computed by means of a direct Monte Carlo simulation of neutrino transport. The radial evolution of the neutrino fluxes in the semitransparent decoupling regions of neutrinos and stellar material is analysed and the results are compared to convenient approximations used in analytical and semi-analytical works. It is shown that local emission and absorption in shocked matter dominates the neutrino flux for at least several tenths of a second after core bounce. The average energy of electron neutrinos drops from about 10 MeV shortly after core bounce to the lower value of about 8 MeV within 300 milliseconds. Electron antineutrinos leave the star with a mean energy of 14 MeV, muon and tauon neutrinos have 16-17 MeV at these early stages of the protoneutron star cooling. The typical time scales for stationary flux pattern to develop in the shocked stellar regions are less than 1 millisecond for electron type neutrinos and about 3 to 4 milliseconds for muon and tauon neutrinos