A ST R O - P H - 9 50 10 05 Gamma - Ray Transfer and Energy Deposition in Supernovae Douglas

Solutions to the energy-independent (gray) radiative transfer equations are compared to results of Monte Carlo simulations of the Ni and Co radioactive decay -ray energy deposition in supernovae. The comparison shows that an e ective, purely absorptive, gray opacity, (0:06 0:01)Ye cm 2 g , where Ye is the total number of electrons per baryon, accurately describes the interaction of -rays with the cool supernova gas and the local -ray energy deposition within the gas. The nature of the -ray interaction process (dominated by Compton scattering in the relativistic regime) creates a weak dependence of on the optical thickness of the (spherically symmetric) supernova atmosphere: The maximum value of applies during optically thick conditions when individual -rays undergo multiple scattering encounters and the lower bound is reached at the phase characterized by a total Thomson optical depth to the center of the atmosphere e < 1. However, the constant asymptotic value, = 0:050Ye cm 2 g , reproduces the thermal light curve due to -ray deposition for Type Ia supernova models to within 10% for the epoch from maximum light to t = 1200 days. Our results quantitatively con rm that the quick and e cient solution to the gray transfer problem provides an accurate representation of -ray energy deposition for a broad range of supernova conditions.