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

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 ∼10 Hz with an FWHM ∼0.6 Hz, and an rms amplitude ∼ 14 per cent. Energy spectra of QPO and non-QPO regimes are also separated and analysed, and the spectra become softer with higher Ecut 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 ∼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.