THE IRON LINE AND HIGH-ENERGY BUMP AS X-RAY SIGNATURES OF COLD MATTER IN SEYFERT-1 GALAXIES

Ginga observations of several bright Seyfert 1 galaxies have recently revealed the presence in their X-ray spectra of both the iron K fluorescence line and a high energy bump, which together are currently interpreted as due to the reprocessing of the primary radiation by cold matter located near the putative black hole. A number of quantitative model predictions on the reprocessed radiation, when the matter is assumed to be distributed in an accretion disk, are presented in this paper; they were obtained, on the basis of Monte Carlo simulations, for different geometries of the disk surface and of the primary X-ray source. The case of a flat disk and a point source placed above the disk on its symmetry axis is treated in greater detail, taking into account the general relativistic and kinematic effects, which have dramatic consequences on the shape of the K line and edge. These effects are less relevant for the equivalent width (W-alpha) of the line and for the strength of the high energy bump, and were therefore ignored for simplicity in computing these two quantities for other source geometries (an optically thin corona, which turns out to be well approximated by the point source, and an optically thick sphere), and for other configurations of the disk surface (conical and concave). Concerning W-alpha, its maximum value is about 150 eV for a flat, 180 eV for a conical and 230 eV for a concave disk seen face-on. Concerning the strength of the bump, it turns out to be an excellent indicator of strong deviations from the planar configuration, and it is shown that, being practically independent of the iron abundance, it can be used to constrain the abundance when used in conjunction with W-alpha. Several observational implications are discussed, in particular it is noted that the relativistic and kinematic effects on the shape of the edge might lead to a misinterpretation of low resolution measurements in terms of absorption by highly ionized iron