| Abstract : | Several Galactic black hole systems show variations in the X-ray flux emitted by the accretion disc present around the black hole. Such variations in frequency space are often seen as broad peaks known as Quasi-periodic oscillations (QPOs). There have been attempts to explain such behavior either by seeking their geometric origin or looking for radiative components that can give rise to them. For the latter one, it is required to analyze the time-averaged spectrum and determine variations in different spectral parameters that can produce observed fractional r.m.s and time lag related to QPOs. In this work, we present a way to do this where spectral parameters are first converted to physical ones to obtain direct interpretation for accretion disks present in such systems. For example, we have chosen AstroSat observations of low-frequency QPOs in GRS 1915+105 and MAXI J1535-571. We found that variations in accretion rate, inner disk radius, coronal optical depth, and heating rate, along with time delays between them, can model the observed energy-dependent behavior. |
