The evolution of the corona in MAXI J1535-571 through type-C quasi-periodic oscillations with Insight-HXMT

TL;DR

This study analyzes the spectral and timing evolution of type-C QPOs in MAXI J1535-571 using Insight-HXMT data, revealing how corona morphology and jet connection change during state transitions.

Contribution

First application of a time-dependent Comptonization model to explain X-ray data up to 100 keV in MAXI J1535-571's intermediate state.

Findings

QPO frequency varies from 2.1 Hz to 9 Hz during state transition.

Corona size and feedback fraction evolve, indicating changing corona morphology.

Possible link between corona evolution and jet activity in the system.

Abstract

Type-C quasi-periodic oscillations (QPOs) in black hole X-ray transients can appear when the source is in the low-hard and hard-intermediate states. The spectral-timing evolution of the type-C QPO in MAXI J1535-571 has been recently studied with Insight-HXMT. Here we fit simultaneously the time-averaged energy spectrum, using a relativistic reflection model, and the fractional rms and phase-lag spectra of the type-C QPOs, using a recently developed time-dependent Comptonization model when the source was in the intermediate state. We show, for the first time, that the time-dependent Comptonization model can successfully explain the X-ray data up to 100 keV. We find that in the hard-intermediate state the frequency of the type-C QPO decreases from 2.6 Hz to 2.1 Hz, then increases to 3.3 Hz, and finally increases to ~ 9 Hz. Simultaneously with this, the evolution of corona size and the feedback fraction (the fraction of photons up-scattered in the corona that return to the disc) indicates the change of the morphology of the corona. Comparing with contemporaneous radio observations, this evolution suggests a possible connection between the corona and the jet when the system is in the hard-intermediate state and about to transit into the soft-intermediate state.