Models of the iron K_alpha fluorescence line and the Compton shoulder in irradiated accretion disk spectra

TL;DR

This paper develops detailed models of accretion disk spectra around supermassive black holes, incorporating Compton scattering and fluorescence, to explain features like iron lines and the Compton Shoulder observed in AGN.

Contribution

It introduces comprehensive model atmosphere equations that include multiple Compton scattering and energy exchange, providing new insights into X-ray spectral features of irradiated accretion disks.

Findings

Identification of the Compton Shoulder contribution to Fe K_alpha line asymmetry

Prediction of limb-brightening effects in reflected X-ray spectra

Reproduction of soft X-ray excess below 1 keV in models

Abstract

We present a full set of model atmosphere equations for the accretion disk around a supermassive black hole irradiated by hard X-ray lamp of power-law spectral distribution. Model equations allow for multiple Compton scattering of radiation on free electrons, and for large relative photon-electron energy exchange at the time of scattering. We present spectra in specific intensities integrated over the disk surface. Theoretical outgoing intensity spectra show soft X-ray excess below 1 keV, and distinct K_alpha and K_beta fluorescent lines of iron. We demonstrate the existence of the Compton Shoulder and claim that it can contribute to the asymmetry and equivalent widths of some observed Fe K_alpha lines in AGN. Our models exhibit the effect of limb-brightening in reflected X-rays.