Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996jkass..29..209m&link_type=abstract
Journal of the Korean Astronomical Society, v. 29 Supplement, p.S209
Physics
1
Accretion, Accretion Disks, Black Hole Physics, Numerical Method, Hydrodynamics, Instability, X-Rays
Scientific paper
This thesis is directed toward an understanding of the physical processes in accretion disks surrounding black holes and neutron stars in X-ray binary sources. In particular, observational phenomena, such as the low frequency (~0.04 Hz) quasi-periodic oscillations (QPOs) in black hole candidates (BHCs: Cyg X-1 and GRO J0422 + 32) and the Rapid Burster MXB 1730-335, and the high frequency QPOs (~3-10 Hz) in BHCs (GX 339-4 and Nova Muscae) are investigated. This study is focused on the structures of stationary disks, their stability and their time variability in the framework of the alpha-viscosity model. It is assumed that the disk is non self-gravitating and axisymmetric, optically thick and geometrically thin so that the vertical direction can be integrated separately. We investigate Keplerian disks by finding the vertical structure solutions with convection included, and subsequently performing nonlinear time-dependent calculations. Detailed examination of the viscosity parameters is presented and it is found that the low frequency QPOs are explicable in terms of a mild thermal-viscous instability. Constraints on the viscosity parameters can be obtained through the observations of QPOs. We have also constructed steady state transonic slim disk models with different viscosity assumptions, i.e., the viscosity vanishes in the supersonic region and the viscous stress is explicitly proportional to the angular velocity gradient. Local stability analysis has been presented and unstable inertial-acoustic modes are identified. These instabilities are studied further through nonlinear time -dependent calculations. We found that, for small values of alpha, the locally unstable modes are globally stable due to the propagation effects. However, for sufficiently large alpha, an oscillatory instability exists in the inner regions of the disk and is restricted to a range of mass accretion rates. The variations of the integrated luminosity from the disk are small. A power spectrum analysis of these variations reveals a low frequency feature at about 4 Hz in one case and which is remarkably similar to those observed in BHCs.
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