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Published July 2022 | Published + Accepted Version
Journal Article Open

Analysis of the reflection spectra of MAXI J1535-571 in the hard and intermediate states


We report results on the joint-fit of the NuSTAR and HXMT data for the black hole X-ray binary candidate MAXI J1535-571. The observations were obtained in 2017 when the source evolved through the hard, hard-intermediate, and soft-intermediate states over the rising phase of the outburst. After subtracting continuum components, X-ray reflection signatures are clearly showed in those observations. By modelling the relativistic reflection in detail, we find that the inner radius Rin is relatively stable with R_(in) ≲ 1.55R_g during the three states, which implies that the inner radius likely extends to the innermost stable circular orbit even in the bright hard state. When adopting R_(in) = R_(ISCO), the spin parameter is constrained to be 0.985_(-0.004)^(+0.002) at 90 per cent confidence (statistical only). The best-fitting results reveal that the inclination of the inner accretion disc is ∼70–74 deg, which notably conflicts with the apparent orientation of the ballistic jet (≤45 deg). In addition, both the photon index and the electron temperature increase during the transition from hard to soft state. It seems that the corona evolves from dense low-temperature in the low/hard state to tenuous high-temperature after the state transition, which indicates that the state transition is accompanied by the evolution of the coronal properties.

Additional Information

© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Received: 14 March 2022. Revision received: 11 May 2022. Accepted: 23 May 2022. Published: 30 May 2022. The authors thank the referee for the helpful comments to improve our manuscript. This work is supported by the NSFC (11773050, 11833007, 12073023), the science research grants from the China Manned Space Project with NO. CMS-CSST-2021-A06. This work used data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This work also used the data from the Insight-HXMT mission, a project funded by China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). The NuSTAR data and software used in this research are provided by the High Energy Astrophysics Science Archive Research Centre (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. DATA AVAILABILITY. Data used in this article are publicly available from the NuSTAR mission (https://heasarc.gsfc.nasa.gov/docs/archive.html) and HXMT mission (http://hxmten.ihep.ac.cn).

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August 22, 2023
October 23, 2023