A NICER look at the state transitions of the black hole candidate MAXI J1535-571 during its reflares

Abstract

The black hole candidate and X-ray binary MAXI J1535-571 was discovered in September 2017. During the decay of its discovery outburst, and before returning to quiescence, the source underwent at least four reflaring events, with peak luminosities of $\sim$10${}^{35-36}$ erg s${}^{-1}$ (d/4.1 kpc)${}^2$. To investigate the nature of these flares, we analysed a sample of NICER observations taken with almost daily cadence. In this work we present the detailed spectral and timing analysis of the evolution of the four reflares. The higher sensitivity of NICER at lower energies, in comparison with other X-ray detectors, allowed us to constrain the disc component of the spectrum at $\sim$0.5 keV. We found that during each reflare the source appears to trace out a q-shaped track in the hardness-intensity diagram similar to those observed in black hole binaries during full outbursts. MAXI J1535-571 transits between the hard state (valleys) and softer states (peaks) during these flares. Moreover, the Comptonised component is undetected at the peak of the first reflare, while the disc component is undetected during the valleys. Assuming the most likely distance of 4.1 kpc, we find that the hard-to-soft transitions take place at the lowest luminosities ever observed in a black hole transient, while the soft-to-hard transitions occur at some of the lowest luminosities ever reported for such systems.

Accepted for publication in MNRAS main journal

References in corpus (23)

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Cited by in corpus (23)

• NICER observations reveal that the X-ray transient MAXI J1348-630 is a Black Hole X-ray binary
• Failed-Transition outbursts in Black hole low-mass X-ray binaries
• The comptonizing medium of the black-hole X-ray binary MAXI~J1535$-$571 through type-C quasi-periodic oscillations
• A variable corona during the transition from type-C to type-B quasi-periodic oscillations in the black hole X-ray binary MAXI J1820+070
• Hard-state optical wind during the discovery outburst of the black-hole X-ray dipper MAXI J1803-298
• Variability and phase lags of the type-C quasi-periodic oscillation of MAXI J1348-630 with NICER
• Discovery of optical and infrared accretion disc wind signatures in the black hole candidate MAXI J1348-630
• A NICER look at the jet-like corona of MAXI J1535-571 through type-B quasi-periodic oscillations
• Wavelet analysis of MAXI J1535-571 with Insight-HXMT
• Analysis of the reflection spectra of MAXI J1535-571 in the hard and intermediate states
• Multiwavelength observations of MAXI J1820+070 during its outburst decay and subsequent mini-outburst
• Seven reflares, a mini-outburst and an outburst : High amplitude optical variations in the black hole X-ray binary Swift J1910.2-0546
• Reflare in MAXI J1348-630]{Evolution of disc and corona in MAXI J1348-630 during the 2019 reflare: NICER and Insight-HXMT view
• Global Accretion Properties of Black Hole X-Ray Binaries: A Phenomenological Perspective
• Clockwise evolution in the hardness-intensity diagram of the black hole X-ray binary Swift J1910.2-0546
• Evolution of Accretion Disk Structure of the Black Hole X-ray Binary MAXI J1820$+$070 during the Rebrightening Phase
• Swift/XRT, Chandra and XMM-Newton observations of IGR J17091-3624 as it returns into quiescence
• The Accretion-Ejection Connection in the Black Hole X-ray Binary MAXI J1820$+$070
• A Multi-wavelength Characterization of the 2023 Outburst of MAXI J1807+132: Manifestations of Disk Instability and Jet Emission
• MAXI J1535-571 2017 outburst Seen by INTEGRAL/SPI and Investigating the Origin of Its Hard Tail
• QPOML: A Machine Learning Approach to Detect and Characterize Quasi-Periodic Oscillations in X-ray Binaries
• A magnetic accretion disk-outflow model for state transition in X-ray binaries
• Broad-band spectral study of LMXB black hole candidate 4U 1957+11 with NuSTAR