Quasi-Periodic Oscillations in Numerical Simulation of Accretion Flows Around Black Holes

We present results of several numerical simulations of two dimensional axisymmetric accretion flows around black holes using the Smoothed Particle Hydrodynamics (SPH). We consider both stellar black holes and as well as supermassive black holes. We assume bremsstrahlung to be the only source of cooling as it is simpler to implement in numerical simulations. We observe that due to both radial and vertical oscillation of shock waves in the accretion flow, the luminosity and average thermal energy content of the inner disk exhibit very interesting behaviors. When power density spectra are taken, quasi-periodic oscillations are seen at a few Hz and also occasionally at hundreds of Hz for stellar black holes. For super-massive black holes, the time-scale of the oscillations ranges from hours to weeks. The power density spectra have usual flat top behavior with average rms amplitude a few percent and a broken power-law behavior. The break frequency is generally found to be close to the QPO frequency as seen in the observed power spectra of black holes. Subject headings: black hole physics — hydrodynamics — accretion, accretion disks — radiative transfer — Instabilities (Submitted to Astrophysical Journal)