Variability of Accretion Disks Surrounding Black Holes ----- The Role of Inertial-Acoustic Instabilities
Session 52 -- Interacting Binaries: Accretion Phenomena
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [52.05] Variability of Accretion Disks Surrounding Black Holes ----- The Role of Inertial-Acoustic Instabilities

Xingming Chen and Ronald E. Taam (Northwestern University)

The global nonlinear time dependent evolution of the inertial-acoustic instability mode in accretion disks surrounding black holes has been investigated. The viscous stress is assumed to be proportional to the gas pressure only, i.e.\,, $\tau = - \alpha p_g$. In this approximation the disk can be thermally and viscously stable. The initial transonic solutions are constructed from the corresponding steady state slim disk equations. It is found that an oscillatory instability exists in the inner regions of the disks for sufficiently large $\alpha$, and is restricted to a range of mass accretion rates. The amplitude of the mass accretion rate modulations at fixed radius, is large and can be a factor of hundred times the steady state value. This variation reflects the changes in the radial velocity instead of the surface density. The integrated luminosity of the disk has small amplitudes variations and its power spectrum can be fitted to a power law function plus a narrow peak centered at a frequency corresponding to the maximum epicyclic frequency of the disk. A lower frequency feature at about 5 Hz can also be seen in some cases. The latter results may be relevant to the temporal variability observed from galactic black hole candidate X-ray sources.