Time-dependent Comptonization - X-ray reverberations

Abstract

We discuss time-dependent Comptonization for a source in which thermal, nonrelativistic Comptonization is an important cooling mechanism. When the scattering optical depth is much larger than the optical depth for emission and absorption of radiation, an impulsive emission within the source is delayed and broadened in time and spectrally hardened, due to repeated Compton scattering. Our treatment allows us to obtain an approximate, analytic solution for the temporal and spectral evolution of a fluctuation and enables us to determine some properties of the source unobtainable from the persistent emission. The results of our calculations may be relevant to X-ray sources showing rapid time variability.