A SEMIANALYTICAL SOLUTION OF THE TRANSFER EQUATION FOR COMPTON REFLECTION MODELS

The method of Lightman and collaborators for the solution of the transfer equation in the Compton reflection problem is generalized to improve and overcome the previous approximations. Numerical computations are required, but they can be largely standardized with significant savings of computing time. This fact helps in the exploration of wide ranges of the model parameters. The emphasis is on the dependence of the X-ray continuum spectrum on the geometry of the primary source, the viewing angle and the electron temperature, and on the reprocessing in the disc of the primary absorbed radiation. The two geometries most frequently used, the semi-isotropic illumination and the illumination from a central point source, for the two extreme cases of completely neutral and fully ionized matter, are compared. The dependence on the viewing angle is found to be quite different in the two geometries. This property has a direct impact on the method of comparing Compton reflection models with observational data of AGN in order to estimate the fraction of reflected radiation. Some implications for the ratio of the ultraviolet to soft X-ray fluxes and for the X-ray background are discussed.