MeerKAT radio non-detection of the X-ray transient EP260531a

ATel #17844; F. J. Cowie (University of Oxford), I. Heywood (University of Oxford and Rhodes University), R. Fender (University of Oxford and University of Cape Town), S. Motta (INAF-OAB) for the X-KAT collaboration
on 15 Jun 2026; 12:48 UT
Credential Certification: Sara Elisa Motta (sara.motta@physics.ox.ac.uk)

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ATel #17828 reported the discovery of EP260531a, a new X-ray transient steadily increasing in flux from May 31st to June 3rd 2026. ATel #17833 reported a refined localisation and continued brightening on June 4th 2026. ATel #17840 identified a potential NIR counterpart to the X-ray transient. The low galactic latitude, X-ray properties, and candidate NIR counterpart of the source suggested a potential X-ray binary nature, and so we triggered follow-up radio observations with the MeerKAT telescope as part of the X-KAT program.

The field of EP260531a was observed for 10 minutes on June 7th starting at 20:12:49 UT (MJD 61198.8422). Observations were carried out at a central frequency of 1.28 GHz, with a total (un-flagged) bandwidth of 856 MHz. PKS B1934-638 was used for flux and bandpass calibration, while J1830-3602 was used for complex gain calibration. No radio source was detected within the 10 arcsecond error circle of the X-ray position (ATel #17833). Given the RMS within this region of ~50 μJy/beam, we report a 3-sigma upper limit of ~150 μJy for the flux density of the source at 1.28 GHz. 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.