Time-dependent calculations of X-ray and gamma-ray reprocessing

Numerical calculations of the reprocessing of high-energy X-ray and gamma-ray radiation (from 1 keV to 1 MeV) have been performed. The incident radiation is assumed to be instantaneously deposited in a hydrostatic stellar atmosphere, changing both the temperature and ionization structure. A fully implicit numerical method is then used to solve the nonlinear diffusion equation for the transfer of the reprocessed radiation. The results of 38 numerical models are presented. Model parameters that were varied include the effective temperature and gravity of the absorbing star and the fluence and spectral temperature of the incident high-energy radiation. For each model, the time to reemit 50 and 99 percent of the incident radiation energy is tabulated. Model results are compared to the extensive observations of coincident X-ray and optical bursts and to the recent reports of correlated gamma-ray burst and optical emission.