DeNisco, Kenneth R.

We examine the effects of general relativity on neutrino transport during the critical shock reheating phase of core collapse supernovae. We derive the equations for general relativistic, static, multi-group, flux-limited diffusion (MGFLD), and use these to modify a Newtonian MGFLD code. The steady-state neutrino distributions calculated by the revised code for several post-collapse stellar cores are compared to those computed with the original Newtonian MGFLD code. The general relativistic transport calculations display the expected reductions in neutrino rms energy and luminosity arising from redshift and curvature effects. Although the effects of general relativity on neutrino transport work against the shock revival, firm conclusions cannot be drawn at this time because of other important general relativistic effects on the structure of the core. Nevertheless, it is clear that modeling with Newtonian transport has little connection to reality.

This work is a simulation of a 15 solar mass star from initial core collapse through the formation of the neutrino-driven wind with an eye towards a possible site for the r-process. We use a new radiation hydrodynamics code known as RadHyd, which is a merger of EVH-1 and MGFLD. The EVH-1 code is a piecewise parabolic method, or PPM, Godunov solver with Newtonian gravitation and MGFLD is a sophisticated multi-group, flux-limited diffusion radiation transport code. Core collapse is initiated from a progenitor model S15s7b of Weaver and Woosley. A maximum radius of 2.0 x 10^11 cm is chosen to retain the shock on the grid for the desired duration of the simulation. The stagnated shock is revived after 300 ms by increasing the internal energy between the shock and the gain radius over a period of 50 ms. Boundary conditions provided by the outward moving shock yield a subsonic wind. The progenitor model is evolved with two different explosion energies (1.5 and 2.5 foes) and two sets of neutrino reaction rates. The first set is the standard set from Bruenn [5], whereas the second contains neutrino-nucleon elastic scattering with nucleon recoil and blocking and nucleon bremsstrahlung. In the analysis, we compare the structure differences caused by the different neutrino rates in the time from bounce to 300 ms after bounce, when the energy addition will take place. Finally, we discuss the further evolution of the model and characterize properties of the neutrino-driven wind for the two sets of rates and explosion energies.