X-ray reflection from photoionized media in active galactic nuclei

We calculate the spectrum of X-ray radiation reflected and reprocessed by a partly ionized optically thick medium in an active galactic nucleus. We self-consistently calculate the ionization balance and thermal balance in the medium along with the distribution of X-ray intensity with optical depth. In addition to absorption or scattering of the incident X-rays, we also compute the spectrum of X-rays emitted by the material, including lines, edges, and bremsstrahlung. The albedo of the medium depends primarily on the X-ray ionization parameter (ratio of incident flux to gas density, ξ_x_) and secondarily on the UV flux generated by dissipation inside the disk; we locate the critical range of ξ_x_ over which the albedo increases from small to nearly unity. While the continuum reflection is very weak below 10 keV when ξ_x_ is small, significant fluxes are emitted in atomic lines and edges in this energy range. In the limit of large ξ_x_, the albedo below 10 keV increases, but reflection in this band is never "gray": some photoelectric absorption remains up to rather large values of ξ_x_, while at still higher values, inverse Compton scattering amplifies the soft X-ray flux. These features are sufficiently sharp that current and near-future X-ray experiments should permit diagnostic measures of ξ_x_.