X-rays and soft gamma-rays from Seyferts, radio galaxies, and black-hole binaries

TL;DR

This paper reviews X-ray and soft gamma-ray emissions from accreting black-hole sources, highlighting correlations between spectral features and the implications for source geometry and emission models.

Contribution

It demonstrates that thermal Comptonization models can explain observed spectra and correlations, comparing Seyferts, black-hole binaries, and radio galaxies.

Findings

Thermal Comptonization models fit Seyfert spectra well.

Strong correlation between X-ray slope and Compton reflection.

Different seed photon energies explain spectral differences in systems.

Abstract

Selected topics dealing with X-ray/soft gamma-ray emission from accreting black-hole sources are reviewed. The shape of soft gamma-ray spectra of Seyferts observed by OSSE can be well modelled by thermal Comptonization. A very strong correlation between the X-ray slope and the strength of Compton reflection in these sources can then be explained by thermal Comptonization in vicinity of the reflecting cold media. Similar correlation is seen for the hard state of black-hole binaries, but the strength of Compton reflection at a given X-ray slope is larger than in Seyferts. This appears to be due to seed photons (for Comptonization) emitted by the cold media having larger energies in stellar-mass systems than in Seyferts. Broad-line radio galaxies have hard X-ray spectra with weak reflection, which reflection is similar to that in Seyferts with hard X-ray spectra. Two main models for the source geometry, a hot inner disk surrounded by a cold outer disk, and a dynamic corona above a cold disk, appear about equally viable based on the presently available data.