Two‐Temperature Coronal Flow above a Thin Disk

Abstract

We extended the disk corona model to the inner region of galactic nuclei by including different temperatures in ions and electrons as well as Compton cooling. We found that the mass evaporation rate, and hence the fraction of accretion energy released in the corona, depend strongly on the rate of incoming mass flow from the outer edge of the disk, a larger rate leading to more Compton cooling, less efficient evaporation, and a weaker corona. We also found a strong dependence on the viscosity, with higher viscosity leading to an enhanced mass flow in the corona and therefore more evaporation of gas from the disk below. If we take accretion rates in units of the Eddington rate, our results become independent of the mass of the central black hole. The model predicts weaker contributions to the hard X-rays for objects with higher accretion rate like narrow-line Seyfert 1 galaxies, in agreement with observations. For luminous active galactic nuclei, strong Compton cooling in the innermost corona is so efficient that a large amount of additional heating is required to maintain the corona above the thin disk.