Temporal properties of flares in accretion disk coronae
  Using a non-linear Monte-Carlo code we investigate the radiative response of an accretion disk corona system to static homogeneous flares. We model a flare by a rapid (comparable to the light crossing time) energy dissipation in the corona or the disk.   If the flares originate from the disk, the coronal response to the soft photon shots produces a strongly non-linear Comptonised radiation output, with complex correlation/anti-correlations between energy bands. This behavior strongly differs from those found with usual linear calculations.   Thus any model for the rapid aperiodic variability of X-ray binaries invoking a varying soft photon input as a source for the hard X-ray variability has to take into account the coronal temperature response.   On the other hand, if the flare is due to a violent heating of the corona, when the perturbation time scale is of the order of a few corona light crossing times, the shot spectrum evolves from hard to soft.   This general trend is independent of the shot profile and geometry.   We show that for short dissipation time, the time averaged spectra are generally harder than in steady state situation. In addition, annihilation line and high energy tails can be produced without need for non-thermal processes. 
Julien Malzac, Elisabeth Jourdain