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 nu clei and QSOs, we study the emission spectrum emerging from a vertical disk -corona structure composed of a two-temperature plasma by solving hydrostat ic equilibrium and radiative transfer self-consistently. Our model can nice ly reproduce the soft X-ray excess with alpha (L-v proportional to nu (-alp ha)) of about 1.5 and the hard tail extending to similar to 50 keV with alp ha similar to 0.5. The different spectral slopes (alpha similar to 1.5 belo w 2 keV and similar to0.5 above) are the results of different emission mech anisms: unsaturated Comptonization in the former and a combination of Compt onization, bremsstrahlung, and reflection of the coronal radiation at the d isk-corona boundary in the latter. (C) 2000 Elsevier Science B.V. All right s reserved.