On the origin of accretion flow photon index–quasi-periodic oscillation frequency (Γ–vQPO) relation

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 explain 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 and their correlations were determined. The resonance condition in the range of (0.507-1.248) ± 0.080 indicates that the components of the accretion flow timescales are comparable. The QPO frequency of 0.840-4.961 Hz was obtained. This affirms the TCAF model prediction of the presence of QPO in the accretion flow during the hard spectral states. The components of accretion flow rates are anti-correlated. This suggests that components of the accretion flow interact at varying distances and cause 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 0.973. Hence, the variations/fluctuation of accretion flow/rates seems to be the underlying physical processes/mechanisms responsible for the origin of Γ-vQPO relation in the hard-intermediate spectral state.