On Seyfert spectra and variability

Abstract

We discuss the observational phenomenology of Seyferts from the point of view of the disk model, and argue that the spectral variability may be related to geometrical changes of the cold matter which provides a source of seed photons for Comptonization in a hot central disk. One possible configuration is a model with quasi-spherical accretion in the central part of the disk, with variability determined by the dynamics of the transition zone between the cold and hot disk. The soft excess component appears as a driver of spectral variability and contributes significantly to the source energetics.