Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei II. Vertical Structure of the Disk

Abstract

We have calculated several representative models of vertical structure of an accretion disk around a supermassive Kerr black hole. The interaction of radiation and matter is treated self-consistently, taking into account departures from LTE for calculating both the disk structure and the radiation field. The structural equations are described in detail, and various approximations are discussed. We have demonstrated that departures from LTE are very important for determining the disk structure, even at the midplane, as well as the emergent radiation, particularly for hot and electron--scattering-- dominated disks. We have shown that at least for the disk parameters studied in this paper, NLTE effects tend to reduce the value of the Lyman jump with respect to the LTE predictions, regardless whether LTE predicts an emission or absorption jump. We have studied the effects of various values of viscosity on the model structure and predicted spectral energy distribution. The viscosity is parameterized through a parameter $α_0$ which describes the vertically-averaged viscous stress, two power-law exponents $ζ_0$ and $ζ_1$, and the division point $m_{d}$ between these two forms. The disk structure and emergent radiation is sensitive mainly to the values of $α_0$, while the other parameters influence the disk structure to a much lesser extent. However, although the detailed shape of the predicted spectrum is sensitive to adopted value of $α_0$, the overall appearance of the spectrum is quite similar.