The Spectrum of Massive Thin Accretion Disks: Theory and Observations

Extract

We have made detailed calculations of the structure and the spectrum of massive, geometrically thin “bare” accretion disks. The calculations are for an α-disk with various assumptions on the viscosity law. The radiative transfer was treated with the Eddington approximation for an atmosphere with a vertical temperature gradient. All significant sources of opacity, for T>10⁴K, are included, and all models are found to be optically thick throughout. Spectral modifications due to electron scattering (modified blackbody and comptonization) are not significant in most cases. The requirement of a geometrically thin accretion disk forces a limit of L<0.3L_ed on the accretion rate. Several previous disk calculations violate this limit (Malkan 1983, Czerny & Elvis 1987, Bechtold et al. 1987) and their results are questionable. The surface temperature is close to the effective temperature, even for regions where electron scattering effects are significant. This is due to the vertical temperature gradient and is in contradiction to earlier findings. The angular distribution of the ionizing flux is strongly influenced by general relativistic effects, and can be very different for various disks.