Radio follow-up of the re-brightening of Swift J1753.5-0127

ATel #16568; Noa Grollimund (Universite Paris Cite & CEA Saclay), Francesco Carotenuto (Oxford University), Stephane Corbel (Universite Paris Cite & CEA Saclay & Observatoire de Paris), Rob Fender (Oxford University), Sara Motta, M. Cristina Baglio (INAF-OAB), Gregory R. Sivakoff (University of Alberta) for the X-KAT collaboration
on 3 Apr 2024; 06:18 UT
Credential Certification: S. CORBEL (stephane.corbel@cea.fr)

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The transient black hole low-mass X-ray binary Swift J1753.5-0127 recently underwent an outburst that lasted ~150-160 days, from late September 2023. The source went back to quiescence in early March 2024 (ATel #16427). Recent LCO observations indicate that the source is re-brightening at optical wavelengths, suggesting that a mini-outburst or a new outburst is starting (ATel #16559).

On March 29, the "X-ray Binary New Early Warning System" (XB-NEWS) triggered an alert showing the optical re-brightening of Swift J1753.5-0127 (ATel #16559). Within 24 hours, we scheduled follow-up radio observations with the MeerKAT telescope as part of the X-KAT programme. Swift J1753.5-0127 was observed for 15 minutes starting on March 31 at 01:02:23.5 UT (MJD 60400.048 ± 0.005). Observations were carried out at a central frequency of 1.28 GHz, with a total bandwidth of 860 MHz. We used J1939-6342 for flux and bandpass calibration, and J1733-1304 for complex gain calibration. On March 31, no source was detected at the known position of Swift J1753.5-0127, and we estimated a 3-sigma upper limit of ~64 uJy. We note that during the previous outburst, X-ray and radio detections occurred several days after the optical rise, thus we may be able to detect the source during the next MeerKAT observations. These early radio observations during the rise provide important constraints on the switch on of the jets, which were only possible thanks to the alert from XB-NEWS.

Multi-wavelength observations are encouraged to study the rise of the outburst. Further radio monitoring is planned.

X-KAT is a large MeerKAT open-time programme to observe X-ray binaries in the radio band, performing weekly monitoring of bright, active systems, with capacity for higher cadence observations, and in coordination with large X-ray and optical monitoring programmes. For further information on this programme contact Rob Fender. The Swift follow-up of X-ray binaries is largely performed as part of the SwiftKAT program, which provides quasi simultaneous X-ray coverage of the X-KAT targets.