Discovery of the radio counterpart of MAXI J1750-327 with MeerKAT
ATel #17979; F. J. Cowie (Oxford), R. P. Fender, (Oxford/Cape Town), Sara Motta (INAF), A. K. Hughes (Oxford), M. M. Nyamai (JIVE) for the X-KAT collaboration
on 17 Aug 2026; 10:42 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Sara Elisa Motta (sara.motta@physics.ox.ac.uk)
Subjects: Radio, X-ray, Binary, Black Hole
ATels #17963 and #17964 reported the discovery of a new X-ray transient. ATels #17969 and #17974 reported that the preliminary X-ray timing and spectral properties respectively were consistent with a black hole X-ray binary system interpretation. ATels #17971 and #17977 reported the optical counterpart and localised the position to sub-arcsecond precision.
Following the X-ray trigger, we initiated follow-up radio observations with the MeerKAT radio telescope as part of the X-KAT programme. MAXI J1750-327 was observed for 10 minutes between 15:56:45 and 16:06:37 UTC on August 15th, 2026 (MJD 61267.6644). Observations were carried out at a central frequency of 1.28 GHz (L-band), with a total bandwidth of 856 MHz. J1939-6342 was used for flux and bandpass calibration, and J1830-3602 for phase calibration.
We detect a radio source with a flux density of approximately 14 mJy coincident with the optical localisation in #17971. The detection is highly significant with a background RMS in the image of ~30 μJy beam-1. The radio spectrum of the source is inverted with a preliminary in-band spectral index of α = +0.33 ± 0.06, adopting the convention Sν ∝ να. This and the reported X-ray photon index of +1.91 on the previous day (#17969) are consistent with an X-ray binary in the hard X-ray state.
We will continue monitoring MAXI J1750-327 with the MeerKAT radio telescope. Multi-wavelength observations are encouraged to study the rise of the outburst.
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.
