An analytic function fit to Monte-Carlo X- and gamma-ray spectra from Thomson thick thermal/nonthermal hybrid plasmas

Abstract

We suggest a simple fitting formula to represent Comptonized X- and gamma-ray spectra from a hot ($kT_e \gtrsim 10$ keV), Thomson thick ($τ_T \gtrsim 5$) hybrid thermal/nonthermal plasma in spherical geometry with homogeneous soft-photon injection throughout the Comptonizing region. We have used this formula to fit a large data base of Monte-Carlo generated photon spectra, and provide correlations between the physical parameters of the plasma and the fit parameters of our analytic fit function. These allow us to construct Thomson thick Comptonization spectra without performing computer intensive Monte Carlo simulations of the high-Thomson-depth hybrid-plasma Comptonization problem. Our formulae can easily be used in data analysis packages such as XSPEC, thus rendering rapid $χ^2$ fitting of such spectra to real data feasible.