On the possible nature of the source of x-ray radiation in quasars

Abstract

The possible nature of the source responsible for X-rays in quasars is discussed. High luminosity accretion disks around supermassive black holes are considered according to the approach which is somewhat different from the standard accretion disk theory. X-ray spectra of quasars are known to be like the X-ray spectrum of the galactic X-ray source Cyg X-1 (Pozdnyakov L. A. et al., 1983, Inoue, H., 1989). It points to the similarity of the physical conditions in the radiating plasma of these objects. We shall show that in the framework of the a-disks theory (Shakura N. & Sunyaev R., 1973) there exist high (-lO'K) temperature solutions, being independent of the central object's mass. We shall consider high luminosity (-&dd) accretion disks around supermassive (-109Ma) black holes in the zone where radiation pressure is dominant. Our approach differs from the standard accretion disks theory in the following points: 1. Radiation pressure is considered exactly, and it is not considered the LTE approximation: Prad # bT4. 2. Radiation transfer is considered in the Eddington approximation with the Compton effect included, and it is not considered in the diffusion approximation. These differences lead to modification of the temperature structure of accretion disks only, and two high temperature solutions may appear under certain conditions, in addition to the known solution. They exist because a cooling function A( T) has a local minimum at T - lo6 K, and when the energy generation rate becomes greater than the cooling rate at T - lo6 K on the given disk radius, two additional solutions appear. We may write the balance of thermal energy equation for these high temperature states: Using Tuker's (1975) analytical approximation for A( T), we find two solutions: T, = 1.47~109a20--1~~ ~-3~2 (2)