The Monte Carlo Simulation of the X-Ray Spectra from the Black Hole X-Ray Binaries

Abstract

The accretion mode of the black hole X-ray binaries (BHXBs) during the intermediate state remains unclear as it corresponds to an unstable situation. In order to find possible observable clues of the accretion mode, we describe all the possible cases with the same set of parameters, and compare the differences of the X-ray spectra for different values of the parameters. Since the geometry of the accretion flow is complex, we adopt the Monte Carlo simulations to obtain output spectra. Different to previous study, the thickness of the cold gas, which is usually ignored, is taken into account. It is found that for the cases with small clouds or a large amount of clouds, the influence of the thickness are significant since the area of the side surface are comparable to the upper surface area. For the thermal component of the output spectra, or the multi-color black-body spectra, the range of the spectral index is larger. While for the power-law component due to inver Compton scattering, the flux can be increased by a few times, which means higher cooling rate of the hot gas and shorter duration of the intermediate state.