Temperature Distributions of Accretion Disks in Active Galactic Nuclei

We present a simple analytical method to determine the temperature distribution of optically thick accretion disks on the basis of the spectral shape of the big blue bump in an active galactic nucleus (AGN). The method is general and does not require the disk to be Keplerian, stationary, or even conservative (without mass loss). Eight AGNs observed with IUE, ROSAT, and Ginga have been studied with this method. We calculate the outer radii of disks corresponding to the dust evaporation temperature, and we find that the radial scale R changes with a frequency ν as R is proportional to ν^-(~1.8~2.2)^. The temperature profiles are derived and discussed within the framework of accretion disk models. The mass of the central black hole can be evaluated from the derived temperature distribution