THE TRANSITION LAYER BETWEEN THE THIN ACCRETION DISK AND THE HOT CORONA: CONSTRAINTS FROM THE THERMAL X-RAY LINE EMISSION

Abstract

The observed continuum spectra in the low-luminosity active galactic nuclei, M81, can be reproduced by the advection-dominated accretion flow (ADAF)+thin disk/corona accretion flow model. We find that the best fit to the spectral energy distribution of M81 requires accretion rate for R tr = 60 R S. The observed H-like and He-like iron lines may probably be emitted from the transition layer between the vertically connected hot corona and cold thin disk. We model a power-law function of height z for the electron temperature in the transition layer, and calculate the thermal H-like and He-like iron line emission from M81. Combining the observations with our results, we find that the thickness of the transition layer is ~14%-23% of the thickness of the corona at the same radius. We discuss that the observed stronger H-like line emission than He-like line emission cannot be explained with the pure ADAF model. Our results provide useful constraints on the theoretical model for disk-corona connection.