The effects of photoionization on X-ray reflection spectra in active galactic nuclei

Abstract

Recent work on the X-ray spectra of Seyfert galaxies has shown the presence of a reflection component due to the hard X-ray continuum scattering from, and causing fluorescence by, cold matter. The strength of the reflection spectrum is usually consistent with the hard X-rays being emitted above a flat accretion disk. In this paper we calculate reflection spectra for cases where the hard X-rays photoionize the surface layers of the disk to the extent that the main X-ray absorbers are significantly ionized. The temperature, ionization state and spectrum are computed in a fully self-consistent manner for the inner, radiation pressure dominated part of an accretion disk. The reflection spectra are steeper, when the accretion rate exceeds 10 percent of the Eddington value, than the incident continuum in the soft X-ray band; they are also rich in emission lines, which may prove to be good diagnostics of the conditions of the inner regions around accreting black holes.