LCO observes the return to quiescence of Swift J1753.5-0127

ATel #16818; Kevin Alabarta, David M. Russell, D. M. Bramich, Sandeep Rout and Payaswini Saikia (NYU Abu Dhabi), M. Cristina Baglio (INAF-OAB), Jeroen Homan (Eureka Scientific), and Fraser Lewis (Faulkes Telescope Project & Astrophysics Research Institute, LJMU)
on 18 Sep 2024; 15:07 UT
Credential Certification: Kevin Alabarta (kalabarta@nyu.edu)

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The black hole low-mass X-ray binary Swift J1753.5-0127 started an outburst in June 2005 (ATel #546) that lasted eleven years until November 2016 (ATel #9735, #9739, #9741, #9758, #9765). A few months later, in February and April 2017, the system underwent two re-brightenings (ATel #10075, #10081, #10097, #10110, #10114, #10288, #10325, #10664). The most recent outburst of Swift J1753.5-0127 was first detected on September 28, 2023 (MJD 60215.10, ATel #16262) with the Las Cumbres Observatory (LCO) network and lasted until March 08, 2024 (MJD 60377.79, ATel #16527). The source then re-brightened again, starting a mini-outburst on March 18, 2024 (MJD 60387.6), with a magnitude at the time in the i' band of 20.69+/-0.08 (ATel #16559).

Here, we report updated source evolution with LCO. Swift J1753.5-0127 increased its optical brightness until it reached a plateau that lasted more than two months (from April to June 2024) at average magnitudes of g' = 17.23 +/- 0.05, V = 17.11 +/- 0.09, r' = 16.93 +/- 0.04, R = 16.75 +/- 0.09, i' = 16.80 +/- 0.15 and zs = 16.68 +/- 0.08. Then, the optical flux of the source decayed until July 5, 2024 (MJD 60496.27), dropping to magnitudes of g' = 19.99 +/- 0.07, r' = 19.14 +/- 0.03, i' = 18.81 +/- 0.04 and zs = 18.55 +/- 0.05.

The next two LCO observations, on July 12, 2024, and July 20, 2024 (MJD 60503.42 and MJD 605111.26, respectively), showed that Swift J1753.5-0127 brightened up to g' = 18.74 +/- 0.04, r' = 18.27 +/- 0.01, i' = 18.00 +/- 0.01 and zs = 17.83 +/- 0.02, to fade again after that date. On September 03, 2024 (MJD 60556.23), the source reached a magnitude in the i' band (21.02 +/- 0.14), which indicates that the source decayed to its pre-outburst levels (i' = 21.37 +/- 0.28; dark red line and shaded area in the figure below). The magnitudes of the source that day in the other bands were r' = 21.39 +/- 0.12 and zs = 20.42 +/- 0.12. The latest observations occurred on September 9, 2024 (60562.29), and the magnitudes of Swift J1753.5-0127 were r' = 21.68 +/- 0.19, i' = 20.88+/- 0.15 and zs = 20.15 +/- 0.11.

Comparing the recent mini-outburst with that occurring in 2017 after the first long (11-year) outburst (Zhang et al. 2019), we find that both are very similar. During the plateau of both mini-outbursts, Swift J1753.5-0127 reached similar magnitudes (V ~ 17 and i' ~ 16.8). Moreover, they had a similar duration (~90 days for the mini-outburst of 2017 and ~100 days for the one of 2024). Finally, both events showed a reflare during their decaying phase, although the reflare of the 2017 mini-outburst was ~0.5 magnitudes brighter in the i' band and displayed a two-peak shape light curve.

Multi-wavelength observations of Swift J1753.5-0127 during quiescence are encouraged. We will continue to observe the system with LCO.

The LCO observations of Swift J1753.5-0127 are performed as part of an ongoing monitoring program of ~50 low-mass X-ray binaries (Lewis et al. 2008). LCO images are processed and reduced, and magnitudes are extracted and calibrated using a real-time data analysis pipeline, the "X-ray Binary New Early Warning System" (XB-NEWS; see Russell et al. 2019, Goodwin et al. 2020 and ATel #13451 for details).

This material is based upon work supported by Tamkeen under the NYU Abu Dhabi Research Institute grant CASS (Center for Astrophysics and Space Science).

LCO optical light curves of Swift J1753.5-0127