MeerKAT radio non-detection of the neutron star X-ray binary EXO 0748-676

ATel #16651; F. Carotenuto (University of Oxford), R. Fender (University of Oxford and University of Cape Town), L. Rhodes (University of Oxford), G. R. Sivakoff (University of Alberta), A. Hughes (University of Alberta), T. D. Russell (INAF/IASF Palermo)
on 14 Jun 2024; 08:37 UT
Credential Certification: Francesco Carotenuto (francesco.carotenuto@cea.fr)

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After 16 years in quiescence (Atel #1812, #1816), the neutron star X-ray binary EXO 0748-676 entered a new bright outburst phase reported in the X-rays with Swift/BAT and XRT (GCN Circular 36653) and in the optical with LCO (ATel #16646). ATLAS archival observations show that the source has been rising since April 2024, roughly two months before the X-ray detection (ATel #16648, #16649).

Within 10 hours of the Swift alert, we triggered follow-up radio observations with the MeerKAT telescope as part of the X-KAT programme. EXO 0748-676 was observed for 15 minutes on June 10th starting at 17:19:20 UT (MJD 60471.72). Observations were carried out at a central frequency of 1.28 GHz, with a total (un-flagged) bandwidth of 860 MHz. We used PKS B1934-638 for flux and bandpass calibration, while we used J0906-6829 for complex gain calibration. No source was detected at the known position of EXO 0748-676, and we report a 3-sigma upper limit of ~66 μJy/beam.

Multi-wavelength observations are encouraged to follow the evolution of the outburst. Further radio observations are 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.