MG11 
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Quasi-Periodic Oscillations of Radiations from Astrophysical Black Holes

Shocks in accretion flows can oscillate if the Rankine-Hugoniot conditions are not satisfied. The oscillating post-shock region intercepts varying numbers of soft photons and inverse Comptonization of these photons generate variable number of hard photons which we observe as quasi-periodic oscillations. We present detained numerical simulations of flows including various kinds of cooling processes and show that we can reproduce the observations, including the power-density spectra very accurately. We present solutions around Schwarzschild and Kerr black holes and discuss the differences.

Spectral Properties of Accretion Flows with shock waves

Standing, oscillating and propagating shock waves are common in accretion flows which are non-Keplerian. These shocks are responsible to inject non-thermal charged particles which generate power-law spectrum of synchrotron radiation. These photons and the soft-photons from the pre-shock Keplerian component are inverse Comptonized by post-shock thermal and non-thermal electrons to produce a spectrum up to a few MeV. We discuss how these spectra depends on the flow properties. We also fit a few observed spectrum with our solution. Our approach does not require external source of non-thermal electrons and since the shocks are produced from the same flow parameters, we have the most self-consistent way to generate such a spectrum.

Spiral Shocks as the Candidates for High Frequency QPOs in stellar mass black holes

High Frequency QPOs are enigmatic as they come in pairs. I show that these can be easily explained by having suitable numbers of spiral shocks in the inner disk of the accretion flows. We present results of numerical simulations and explain all the four cases in which 2:3 frequency rations have been observed.

Astrophisical black holes: Do they have boundary layers?