Spectral energy distributions of active galactic nuclei from an accretion disk with advective coronal flow

To explain the broad-band spectral energy distributions (SED) of Seyfert nuclei and QSOs, we study the emission spectrum emerging from a vertical disk-corona structure composed of a two-temperature plasma by solving hydrostatic equilibrium and radiative transfer self-consistently. Our model can nicely reproduce the soft X-ray excess with alpha (L-v proportional to nu (-alpha)) of about 1.5 and the hard tail extending to similar to 50 keV with alpha similar to 0.5. The different spectral slopes (alpha similar to 1.5 below 2 keV and similar to0.5 above) are the results of different emission mechanisms: unsaturated Comptonization in the former and a combination of Comptonization, bremsstrahlung, and reflection of the coronal radiation at the disk-corona boundary in the latter. (C) 2000 Elsevier Science B.V. All rights reserved.