On the energy dependence of the QPO phenomenon in the black hole system MAXI J1535-571

TL;DR

This study investigates how the Quasi-Periodic Oscillation (QPO) frequency in the black hole system MAXI J1535-571 depends on spectral parameters, revealing correlations with scattering fraction and time-lag behaviors, and modeling the physical processes involved.

Contribution

It provides the first detailed analysis of energy-dependent QPO properties and their relation to spectral parameters in MAXI J1535-571, including modeling of time-lags and rms variations.

Findings

QPO frequency correlates with scattering fraction and is consistent with dynamical frequency.

Time-lag between photons changes sign at 2.2 Hz, similar to GRS 1915+105.

Modeling indicates correlated variation of accretion rate, disc radius, and coronal heating.

Abstract

Previous analysis of AstroSat observations of the black hole system MAXI J1535-571, have revealed the presence of a strong Quasi-Periodic Oscillation (QPO) whose frequency is correlated with the high energy spectral index. Here, we fit the spectra as emitted from a truncated disc with an inner hot corona, study the QPO frequency dependence on other spectral parameters and model the energy dependent r.m.s and time-lag of the QPO to identify the physical spectral parameters whose variation are responsible for the QPO. The QPO frequency is found to also correlate with the scattering fraction (i.e. the fraction of the soft photons Comptonized) and its dependence on the accretion rate and inner disc radii is consistent with it being the dynamical frequency. The time-lag between the hard and soft photons is negative for QPO frequency > 2.2 Hz and is positive for lesser values, making this the second black hole system to show this behaviour after GRS 1915+105. Modelling the energy dependent time-lag and r.m.s requires correlated variation of the accretion rate, inner disc radii and the coronal heating rate, with the latter having a time-lag compared to the other two for QPO frequencies less than < 2.2 Hz and which changes sign (i.e. the coronal heating variation precedes the accretion rate one) for higher values. The implications of the results are discussed.