ANISOTROPIES IN THE NEUTRINO FLUXES AND HEATING PROFILES IN TWO-DIMENSIONAL, TIME-DEPENDENT, MULTIGROUP RADIATION HYDRODYNAMICS SIMULATIONS OF ROTATING CORE-COLLAPSE SUPERNOVAE

摘要

Using the two-dimensional, multigroup, flux-limited diffusion version of the code VULCAN/2D, which also incorporates rotation, we have calculated the collapse, bounce, shock formation, and early postbounce evolutionary phases of a core-collapse supernova for a variety of initial rotation rates. This is the first series of such multigroup calculations undertaken in supernova theory with fully multidimensional tools. We find that although rotation generates pole-to-equator angular anisotropies in the neutrino radiation fields, the magnitude of the asymmetries is not as large as previously estimated. The finite width of the neutrino decoupling surfaces and the significant emissivity above the τ = 2/3 surface moderate the angular contrast. Moreover, we find that the radiation field is always more spherically symmetric than the matter distribution, with its plumes and convective eddies. The radiation field at a point is an integral over many sources from the different contributing directions. As such, its distribution is much smoother than that of the matter and has very little power at high spatial frequencies. We present the dependence of the angular anisotropy of the neutrino fields on neutrino species, neutrino energy, and initial rotation rate. Only for our most rapidly rotating model do we start to see qualitatively different hydrodynamics, but for the lower rates consistent with the precollapse rotational profiles derived in the literature the anisotropies, although interesting, are modest. This does not mean that rotation does not play a key role in supernova dynamics. The decrease in the effective gravity due to the centripetal effect can be quite important. Rather, it means that when a realistic mapping between initial and final rotational profiles and two-dimensional multigroup radiation hydrodynamics are incorporated into collapse simulations, the anisotropy of the radiation fields may be only a secondary, not a pivotal, factor in the supernova mechanism.