On the origin of Accretion flow Photon index–Quasi-Periodic Oscillation frequency (Γ– vQPO) relation

Abstract MAXI J1535−571 outburst was dramatic and the accretion flow exhibits spectra-temporal characteristics related to one another. In this study, MAXI J1535−571 data observed by SWIFT/BAT (Swift/Burst Alert Telescope) and MAXI/GSC (Monitor of All-sky X-ray Image/Gas slit camera) was analyzed. The physical and phenomenological models that explains the components of the accretion flow were adopted in fitting/modelling the data in XSPEC v12.10.1f. The accretion flow characteristics and photon index–Quasi-Periodic Oscillation frequency (Γ–vQPO) relation were determined, and their correlations were statistically significant. The resonance condition in the range of (0.5076– 1.2481) ± 0.0802 indicates that the components of the accretion flow timescales are comparable and this suggests the presence of QPO. The components of accretion flow rates are anti-correlated and this suggests that they could interact at varying distances and change the distribution of energy spectral indices in the post-shock region/Compton cloud. The photon index–QPO frequency is tightly correlated with a coefficient of 0.97. Hence, the variations/fluctuation of accretion flow rates seem to be the underlying physical processes/mechanisms responsible for the origin of Γ–vQPO relation in the hard-intermediate spectral state.