Wavelet analysis of the transient QPOs in MAXI J1535$-$571 with Insight-HXMT

TL;DR

This study uses wavelet analysis to investigate transient QPOs in MAXI J1535-571, revealing their properties, spectral behavior, and possible connection to jet activity and corona ejection.

Contribution

It introduces wavelet analysis for transient QPO detection and links QPO duration to high-energy count rates and corona dynamics.

Findings

Transient QPOs are type-C and occur in the HIMS.

QPO duration correlates with high-energy count rate.

QPO disappearance may relate to corona ejection.

Abstract

Using wavelet analysis and power density spectrum, we investigate two transient quasi-periodic oscillations (QPOs) observed in MAXI J1535$-$571 observed with Insight-HXMT. The transient QPOs have a centroid frequency of $\sim 10$ Hz with a FWHM $\sim 0.6$ Hz and an rms amplitude $\sim 14\%$. Energy spectra of QPO and non-QPO regimes are also separated and analyzed, and the spectra become softer with higher $E_{cut}$ in the non-QPO regime compared to the QPO regime. Our results suggest that the transient QPOs detected in MJD 58016 and 58017 are still the type-C QPO, and the source remains in its HIMS. The duration of all type-C QPO signals based on wavelet is positively correlated with the mean count rate above $\sim 10$ keV, implying appearance of QPOs in different time scales should be coupled with the corona. The transient QPO properties could be related to the jet or flares, perhaps the partial ejection of the corona is responsible for the disappearance of the type-C QPO.