paper

Broad-Band Spectral Energy Distributions of Active Galactic Nuclei from an Accretion Disk with Advective Coronal Flow

arXiv:astro-ph/0008404 · doi:10.1086/318297

Abstract

We construct a disk-corona model which accounts for the optical-to-X-ray spectral properties of Seyfert nuclei and QSOs. We study emission spectrum emerging from a vertical disk-corona structure composed of two-temperature plasma by solving hydrostatic equilibrium and radiative transfer self-consistently. A fraction of viscous heating is assumed to be dissipated in a corona with a Thomson optical depth of , where advective cooling is also included, and a remaining fraction, , dissipates within a main body of the disk. Our model can nicely reproduce the soft X-ray excess with a power-law shape and the hard tail extending to 50 keV. The different spectral slopes ( 1.5 below 2keV and 0.5 above, where $\Fnu \propto ν^{- α}$) are the results of different emission mechanisms and different sites; the former slope is due to unsaturated Comptonization from the innermost zone and the latter is due to a combination of the Comptonization, bremsstrahlung and a reflection of the coronal radiation at the disk-corona boundary from the inner to surrounding zone ( 300 Schwarzschild radii). The emergent optical spectrum is redder () than that of the standard disk (), being consistent with observations, due to the different efficiencies of spectral distortion of disk emission at different radii. Further, we find that the cut-off frequency of the hard X-ray ( coronal electron temperature) and broad-band spectral shape are insensitive to the black-hole mass, while the peak frequency of the big blue bump is sensitive to the mass as the peak frequency $\propto \Mbh^{-1/4}$.

12 pages, 9 figures, accepted for publication in the Astrophysical Journal

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