AGN Disks Research Articles

Structure of Outer Regions of Accretion Disks in AGN: Non Irradiated, Vertically Averaged Accretion Disks

Radial structure of outer regions of α-disks (Shakura & Sunyaev 1973) is investigated in a more sophisticated way than in Collin-Souffrin & Dumont (1990). The vertically averaged equations for the disk structure hold but some of them are reconsidered : the equation of state (atoms, ions and molecules) with a the rigourous treatment of opacities is introduced. The radiative flux is treated as in Hubeny (1990), and finally a rigourous treatment of the self-gravitaty is included.

The Vertical Structures of Accretion Disks in AGN

Radiation emitted from an accretion disk around a central black hole is the widely accepted model for the observed optical to UV emission from AGN. We have calculated the properties of a standard α-accretion disk (Shakura and Sunyaev, 1973). We present a fully self-consistent model of the structure and the spectrum of such a disk, i.e. the internal vertical density and temperature profiles are calculated simultaneously with the local spectra. Constant density models have been presented by (Ross et al., 1992). The central object is assumed to be a Kerr black hole (BH); relativistic corrections are included. The local energy production is assumed to be entirely due to turbulence. The radiative transfer equation is solved using the Eddington approximation. Inelastic Compton scattering is treated approximately by the Kompaneets equation, and the absorption cross section contains free-free and bound-free processes for hydrogen. The energy transport includes radiation and convection, and the convective flux is calculated in the mixing length theory, taking into account the heating and cooling of the rising elements. Although the convective flux is energetically negligible it has a strong influence on the vertical density structure. We performed several calculations for different parameters such as Ṁ and α. In regions, where the surface radiation flux is large, we get a strong density inversion because the radiation force per unit mass overcomes the gravitational force. Such a density profile, however, is unstable against convection. Including the convective flux then leads to a monotonic density profile. Figures 1 and 2 show the structure and integrated spectrum for two different disk models.

Frequency-Dependent Polarization in Comptonization Models for AGN

The angular distribution and the polarization of radiation as a function of the angle and frequency for the two-phase model of accretion disks in AGN are found. The results depend strongly on the temperature of the hot corona.

Physics of Magnetized Accretion Disks in AGN

Field and Rogers (1993) proposed that the accretion disks in moderate - L AGN (≲ 1044 erg sec−1) are dominated by magnetic stress rather than gas or radiation pressure. A magnetic field parallel to the disk forms loops above and below it where reconnection accelerates electrons to relativistic energies. The nonthermal radiation observed is the synchrotron emission and inverse-Compton scattering by these electrons.

Variability of Black Hole Accretion Disks

We consider two forms of variability in black hole accretion disks: harmonically oscillating modes trapped near the disk inner edge, and noisy fluctuations throughout the entire disk. We apply the former to AGN disks, and the latter to the X-ray power spectra of GX339-4.

Non linear stability of slender accretion disks by bifurcation method

Abstract The nonlinear evolution of a constant angular momentum accretion disk subject to Papaloizou and Pringle (1984; hereafter PP) instability is investigated. The analysis is performed on an inviscid incompressible two-dimensional model using a formalism suitable for Hamiltonian systems. Only the most unstable modes are taken into account. It is found that relevant nonlinear terms have a stabilizing influence on the system. This supports recent numerical experiments showing a transition towards a quasi-stable planet configuration. The extension of the method to fat disk instabilities, more relevant to AGN disks, is discussed.