THE SPECTRA OF ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI

We present fully self-consistent calculations of the spectra emitted by accretion discs in active galactic nuclei. We treat the inner, radiation-pressure-dominated regions of standard alpha-discs. Incoherent Compton scattering and emission/absorption of radiation by hydrogen and helium are included in computing the vertical temperature structure within the disc and the emergent spectrum. Comptonization modifies the EUV/soft X-ray continuum and the He II spectral features. In particular, an important fraction of the emergent luminosity appears in the form of a steep soft X-ray spectrum. We find that the observed UV flux and soft X-ray excess of Mkn 841 are consistent with a face-on accretion disc with alpha = 0.1, surrounding a black hole with M = 2 x 10(7) M. and L = 0.28 L(edd).