Insight-HXMT observations of the New Black Hole Candidate MAXI J1535-571: timing analysis

TL;DR

This paper analyzes the timing properties of the black hole candidate MAXI J1535-571 during its 2017 outburst using Insight-HXMT data, revealing state transitions, QPO characteristics, and energy-dependent timing features.

Contribution

It provides detailed timing analysis of MAXI J1535-571, including QPO energy dependence and phase lag behavior, utilizing Insight-HXMT's high-energy capabilities for the first time.

Findings

Detection of state transitions from LHS to SIMS.

Observation of energy-dependent QPO amplitude and frequency up to 100 keV.

Identification of negative phase lags correlated with QPO centroid frequency.

Abstract

We present the X-ray timing results of the new black hole candidate (BHC) MAXI J1535-571 during its 2017 outburst from Hard X-ray Modulation Telescope (\emph{Insight}-HXMT) observations taken from 2017 September 6 to 23. Following the definitions given by \citet{Belloni2010}, we find that the source exhibits state transitions from Low/Hard state (LHS) to Hard Intermediate state (HIMS) and eventually to Soft Intermediate state (SIMS). Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of \emph{Insight}-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV which is rarely explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lags) and strongly correlated with the centroid frequency. By assuming a geometrical origin of type-C QPOs, the source is consistent with being a high inclination system.