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

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.