  Short-term variability of X-ray spectra has been reported for several Active
Galactic Nuclei. Significant X-ray flux variations are observed within time
scales down to 10^4 -- 10^5 seconds. We discuss short variability time scales
in the framework of the X-ray flare model, which assumes the release of a large
hard X-ray flux above a small portion of the accretion disk. The resulting
observed X-ray spectrum is composed of the primary radiation as well as a
reprocessed/Compton reflection component that we model performing numerical
radiative transfer simulations. We conduct Monte-Carlo simulations of large
flare distributions across the disk including relativistic corrections of the
observed radiation and discuss general implications on AGN spectra and their
variability.
