The W-K Relation in Black Hole X-ray Binaries from Insight-HXMT Observation

Through decades of observations and studies, the characteristics of black hole X-ray binaries (XRBs) have been gradually revealed. However, the structure of the accretion disk remains uncertain. In the power density spectrum of the BHXRB (Black Hole X-ray Binaries), there is a correlation between the break frequency and the quasi-periodic oscillation (W-K relation), and it can constrain the current model of accretion disk. The W-K relation in black hole XRBs is studied based on the observations of five black hole XRBs by Insight-HXMT (Hard X-ray Modulation Telescope). The result shows that the W-K relation is valid in all the three telescopes with different energy bands. Moreover, a correlation between the break frequency and the inner radius of the accretion disk is found for MAXI J1535-571, which is self-consistent with the model of a truncated accretion disk. If the observed power density spectra result from the propagation of perturbation in mass accretion rate, it can be further inferred that the inner radius of the accretion disk is close to the innermost stable circular orbit and the black hole might be a high-spin system.