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

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 exact location of the matter in relation to the hard X-ray source is unclear, but the strength of the reflection spectrum is usually consistent with the hard X-rays being emitted above a flat accretion disc. In this paper we calculate reflection spectra for cases where the hard X-rays photoionize the surface layers of the disc 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 disc. The effects of photoionization are important typically when the accretion rate exceeds 10 per cent of the Eddington value. The reflection spectra are then steeper than the incident continuum in the soft X-ray band and are rich in emission lines which may prove to be good diagnostics of the conditions of the inner regions around accreting black holes. Reflection spectra from sources around stellar-mass black holes are also presented. The weak iron emission-line characteristic of these objects is explained.