Rapidly Evolving Disk–Jet Coupling during Re-brightenings in the Black Hole Transient MAXI J1535−571

Abstract

The main outburst of the candidate black hole low-mass X-ray binary (BH LMXB) MAXI J1535−571 ended in 2018 May and was followed by at least five episodes of re-brightenings. We have monitored this re-brightening phenomenon at X-ray and radio wavelengths using the Neil Gehrels Swift Observatory and Australia Telescope Compact Array, respectively. The first two re-brightenings exhibited a high peak X-ray luminosity (implying a high mass accretion rate) and were observed to transition from the hard to the soft state. However, unlike the main outburst, these re-brightenings did not exhibit clear hysteresis. During the re-brightenings, when MAXI J1535−571 was in the hard state, we observed the brightening of a compact radio jet which was subsequently quenched when the source transitioned to a similar soft state as was observed during the main outburst. We report on the first investigation of disk-jet coupling over multiple rapidly evolving re-brightenings in a BH LMXB. We find that the accretion flow properties and the accompanying compact jet evolve on a similarly rapid time scale of ∼days rather than the typical value of ∼weeks as observed for most other BH LMXBs during their main outburst events.

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

“…Finally, we found that each reflare is fainter than the preceding one (see also Parikh et al 2019a and Section 4.3 for further discussion), albeit their duration appears to remain approximately constant (∼30 days). Additionally, we observe that the disc component follows the same behaviour, as it can be inferred from both spectral and timing parameters.…”

“…The reflares in J1535 also displayed hysteresis in the HID, suggesting similar state transitions that we then demonstrated with our spectral fits. Swift/XRT observations of these flares also suggested state transitions (Parikh et al 2019a); however the Swift/XRT data quality did not allow the authors to detect the hysteresis loops. The reflares hysteresis loops occur at 100 times lower luminosities than the main peak of the outburst.…”

“…After reflare 4, the count rate remained at a low value, similar to that reached before the reflaring events, at an average luminosity of ∼10 34 erg s −1 for ∼15 days. In the last ∼3 days before the 2018 Sun constraint, the count rate started to increase again, strongly suggesting the onset of a fifth reflare (see Parikh et al 2019a). The overall behaviour of the Swift/XRT light curve of J1535 (bottom panel of Figure 1) is, as expected, very similar to the NICER light curve, although with a poorer sampling.…”

“…The first rebrightening of J1535 was detected in mid May, 2018, by Parikh et al (2018) at 0.5−10 keV, and the fits to these data suggested that the source may have transitioned to the soft state. A total detection of 5 reflaring episodes, during the outburst declining, was reported by Parikh et al (2019a) from Swift and ATCA data. The source was no longer detected since May 2019 (Parikh et al 2019b).…”

“…According to the classification of Zhang et al (2019) for different types of rebrightenings, the events in J1535 are reflares, which is the term we will use from now on. However, Parikh et al (2019a) consider that the source had returned to quiescence before the rebrightening episodes, making J1535 to lie outside of this classification.…”