Local thermal instability and the warm corona: hot or not?

We aim to study whether the model of warm X-ray corona, heated by the magnetic field emerging from the disk, can explain the Soft X-ray Excess observations in Active Galactic Nuclei. Utilizing our model that solves a one-dimensional vertical structure of a magnetized accretion disk, we are able to obtain the temperature and optical depth of the warm corona. Comparing these results to observations, we obtain a satisfactory agreement. In-depth analysis shows that the lower boundary of a thermally unstable region predicts very well the observations for some range of accretion rates. We conclude that the accuracy of this prediction, if not coincidental, is very curious, and warm corona might be tightly linked to thermal instability.