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Low and intermediate frequency quasi-periodic oscillations (QPOs) in blackhole candidates are believed to be due to oscillations of the Comptonizingregions in an accretion flow. Assuming that the general structure of anaccretion disk is a Two Component Advective Flow (TCAF), we numericallysimulate the light curves emitted from an accretion disk for differentaccretion rates and find how the QPO frequencies vary. We use a standardKeplerian disk residing at the equatorial plane as a source of soft photons.These soft photons, after suffering multiple scattering with the hot electronsof the low angular momentum, sub-Keplerian, flow emerge out as hard radiation.The hydrodynamic and thermal properties of the electron cloud is simulatedusing a Total Variation Diminishing (TVD) code. The TVD code is then coupledwith a radiative transfer code which simulates the energy exchange between theelectron and radiation using Monte Carlo technique. The resulting localizedheating and cooling are included also. We find that the QPO frequency increasesand the spectrum becomes softer as we increase the Keplerian disk rate.However, the spectrum becomes harder if we increase the sub-Keplerian accretionrate. We find that an earlier prediction that QPOs occur when the infall timescale roughly matches with the cooling time scale, originally obtained using apower-law cooling, remains valid even for Compton cooling. Our findings agreewith the general observations of low frequency QPOs in black hole candidates.

Quasi Periodic Oscillations in a Radiative Transonic Flow: Results of a Coupled Monte Carlo-TVD Simulation