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Description
MAXI J1535-571 outburst evolution is driven by physical mechanisms that mediate the accretion flow dynamical behavior/characteristics. In this study, MAXI J1535-571 data observed by MAXI/GSC, NuSTAR, and SWIFT/BAT, were analyzed using HEASoft v6.2 and its software packages. Spectral fitting/modelling was done in XSPEC v12.10.1f using phenomenological and physical models. MAXI J1535-571 X-ray spectra with an acceptable statistical fit and reduced Chi-squared value of ≤ 1.1 were obtained. Accretion flow characteristics and their correlations were determined. The components of the accretion flow/rates show variations/fluctuations at different epochs. This indicates the dynamical behavior of the accretion flow and its geometry is “sombrero” or patchy-flaring turbulence flow. The decrease in accretion rate ratio (ARR) and shock location (Xs) shows that the outburst evolution progresses on timescales. A compression ratio (R) of 3.998 shows that the oscillating waves in the accretion flow are strong. The resonance condition of (0.507–1.248) ± 0.024 indicates that the timescales of components of the accretion flow roughly matched. The Quasi-Periodic Oscillation frequency (vQPO) of 0.560–4.961 Hz was obtained. This suggests a type-C QPO signature seen in the hard spectral states. Moreover, the components of the accretion flow/rate variations/fluctuations caused a distribution of energy spectral indices (α = Γ – 1) in the post-shock region/Compton cloud. The track of photon index (Γ)–vQPO relation was determined. This is consistent with the previous studies. Hence, mass accretion rate variations/fluctuations caused the decrease in the ARR, shock location, and perhaps, delay in a transition period as the outburst progresses. Therefore, mass accretion rate variations/fluctuations seem to be the underlying physical mechanisms responsible for the origin of Γ–vQPO relation, X-ray flux variability, and spectral evolution of MAXI J1535-571.
Keywords: MAXI J1535-571; accretion flow, mass accretion rate variations/fluctuations; Γ–vQPO relation, X-ray flux variability/spectral evolution, accretion flow geometry.
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