Neutrino heating, convection, and the mechanism of Type-II supernova explosions.

Abstract

The role of neutrino heating and convective processes in the explosion mechanism of Type-II supernovae is investigated by one- and two-dimensional hydrodynamical simulations of the long-time evolution of the collapsed stellar core after the bounce at nuclear matter density and after the associated formation of the supernova shock. The parameters describing the neutrino emission from the collapsed stellar core are systematically varied. The possibility to obtain explosions turns out to be very sensitive to the physical conditions in and at the protoneutron star, in particular to its contraction and to the neutrino cooling inside of the gain radius. Yet, above a certain threshold for the core neutrino luminosity, stable and energetic explosions can be obtained in spherical symmetry, provided the energy deposition by neutrinos remains strong for a sufficiently long period. The explosion energy and time scale critically depend on the neutrino fluxes during the shock revival phase and on their temporal decay during the first few 100 ms after shock formation. The threshold luminosity is a very sensitive function of the shock stagnation radius, because small radii of the stalled prompt shock lead to significantly higher neutrino loss from the hot and compact postshock layers, cause the region of neutrino heating to be very narrow, and reduce the heating time scale of the matter due to the high infall velocity. (orig.)