X-ray reflections on AGN

Abstract

X-ray reflection generates much of the spectral complexity in the X-ray spectra of AGN. It is argued that strong relativistic blurring of the reflection spectrum should commonly be expected from objects accreting at a high Eddington rate. The good agreement found between the local density in massive black holes and the energy density in quasar and AGN light requires that the accretion which built massive black holes was radiatively efficient, involving thin discs extending within 6 gravitational radii. The soft excess found in the spectra of many AGN can be explained by X-ray reflection when such blurring is included in the spectral analysis. Some of the continuum variability and in particular the puzzling variability of the broad iron line can be explained by the strong light bending expected in the region immediately around a black hole. Progress in understanding this behaviour in the brightest sources can be made now with long observations using instruments on XMM-Newton and Suzaku. Future missions like Xeus and Con-X, with large collecting areas, are required to expand the range of accessible objects and to make reverberation studies possible.