Gamma-Ray Transfer and Energy Deposition in Supernovae

Solutions to the energy-independent (gray) radiative transfer equations arecompared to results of Monte Carlo simulations of the \Ni and \Co radioactivedecay \GR energy deposition in supernovae. The comparison shows that aneffective, purely absorptive, gray opacity, \KG $\sim (0.06 \pm 0.01)Y_e$cm$^2$ g$^{-1}$, where $Y_e$ is the total number of electrons per baryon,accurately describes the interaction of \GRs with the cool supernova gas andthe local \GR energy deposition within the gas. The nature of the \GR\interaction process (dominated by Compton scattering in the relativisticregime) creates a weak dependence of \KG on the optical thickness of the(spherically symmetric) supernova atmosphere: The maximum value of \KG appliesduring optically thick conditions when individual \GRs undergo multiplescattering encounters and the lower bound is reached at the phase characterizedby a total Thomson optical depth to the center of the atmosphere \te \LA 1. Ourresults quantitatively confirm that the quick and efficient solution to thegray transfer problem provides an accurate representation of \GR energydeposition for a broad range of supernova conditions.Comment: 24 pages, PostScript file including 9 figures. Accepted for publication in The Astrophysical Journa