Including a Warm Corona within the Inner Accretion Disk of Active Galactic Nuclei

Abstract

Warm coronae, Comptonizing regions of warm (temperature kT ∼ 1keV), and optically thick (Thomson depth ∼ 10 - 20) gas, at the surfaces of accretion disks in active galactic nuclei (AGNs), have been proposed to explain the origin of the soft X-ray excess commonly observed in the X-ray spectra of AGNs. We calculate the X-ray emission from an irradiated constant density accretion disk atmosphere that includes heating from a warm corona, as well as illumination from an external X-ray power-law radiation, and blackbody emission from the dissipation in the accretion disk. The model accounts for the radial dependence of disk ionization, including the effects of light-bending on the illuminating X-rays. The final spectra are produced by integrating the local reflection/emission spectrum from approximately 2 to 400 gravitational radii. We demonstrate how the soft excess in AGN X-ray spectra depends on the warm corona parameters, including the heating fraction and optical depth, and the strength of the X-ray illumination. The model will be publicly released in 2022 for use in fitting AGN spectra.