Emission Spectrum Integrated over an Accretion Disk: Comparison with Observations of Active Galactic Nuclei

Abstract

Emission spectrum from an accretion disk for active galactic nuclei is obtained by solving the vertical structure and radiative transfer self-consistently and by integrating the local spectrum over radii. We found that even for moderate accretion rates, disks emit a significant portion of the total luminosity in UV through soft X-ray range; for the accretion rate close to the Eddington limit, soft X-ray luminosity for a 0.1-2.0 keV range amounts to 57%, 43%, and 33% of the total luminosity for a black hole mass of 10⁷, 10⁸, and 10⁹ M_sun, respectively. We compared our numerical results with lUE, Einstein, EXOSAT, and ROSAT observations of low-redshift quasars and Seyfert 1 galaxies and found that our results can statistically account for observations of the UV bump and soft X-ray excess simultaneously without exceeding the Eddington limit. We also performed a detailed spectral fit to the quasar H1821 + 643, for which the estimated values of the black hole mass and accretion rate are 1.5 × 10⁹ M_sun and 0.7L_Edd, respectively.