Speaker
Description
Soft X-ray excess, observed in Active Galactic Nuclei and Black Hole Binaries is often explained by the model of warm, optically thick layer. The photons from underlying disk cool the corona, and their energy gain can be observed as an excess over the power law at energy of around 1 keV. Warm corona has been successfuly modeled using many approaches, but the parameters obtained from the observations also are on the edge of region in the parameter space where the structure becomes suspicible to thermal instability and condensation to clumps. Warm corona is observed commonly in AGN, which means that the instability cannot completely hinder its formation. We discuss points for and against occurence of this phenomenon and propose scenarios that could explain the apparent discrepancy between models and observations.