MeerKAT radio detection of GRS 1739-278 during its recent outburst

ATel #16116; Andrew Hughes (U. Alberta), Thomas Russell (INAF-IASF Palermo), Rob Fender (Oxford), Patrick Woudt (U. Cape Town), James Miller-Jones (Curtin), on behalf of the ThunderKAT collaboration
on 3 Jul 2023; 17:23 UT
Credential Certification: Thomas Russell (thomas.russell@inaf.it)

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The candidate black hole X-ray binary GRS 1739-278 has recently shown renewed X-ray activity characteristic of a new outburst. The outburst was initially detected by MAXI on 2023 June 26 (ATel #16097). Following the detection, Swift-XRT observations confirmed that MAXI had detected GRS 1739-278. Modelling of the X-ray spectrum suggested that the source had transitioned into the soft accretion state (ATel #16100). Furthermore, the LEIA X-ray telescope revealed that the source had been in an outbursting state since 2023 June 22 (ATel #16102). Following recent reports of the X-ray detections of the source, we observed GRS 1739-278 with the MeerKAT radio telescope as part of the ThunderKAT Large Survey Programme (Fender et al. 2017). Observations were carried out at a central frequency of 1.28 GHz, with a total bandwidth of 860 MHz. We used PKS J1939-6342 for flux and bandpass calibration, and J1833-2103 for complex gain calibration.

GRS 1739-278 was observed for 15 minutes on 2023 June 30 between 01:27:49 - 01:42:37 (MJD 60125.066 +/- 0.005). We detect radio emission coincident with the known source position. Fitting for a point source in the image plane, we measure a flux density of 1.2 +/- 0.1 mJy (at 1.28 GHz). Radio emission from black hole X-ray binaries originate from relativistic jets (either a steady compact jet or transient jet ejections; Fender & Gallo 2014). However, in the soft accretion state, radio emission from the steady compact jet is strongly quenched (e.g., Fender 1999 et al., Russell et al. 2020). Therefore, the detected radio emission likely originates from a transient jet ejection launched during the transition from the hard accretion state to the soft accretion state.

Further radio monitoring is planned. Multiwavelength follow-up is encouraged.

ThunderKAT will run for 5 years and targets X-ray binaries, Cataclysmic Variables, Supernovae and Gamma-Ray Bursts. As part of this programme, we perform weekly monitoring observations of all bright, active, southern hemisphere X-ray binaries in the radio band. For further information on this programme please contact Rob Fender and/or Patrick Woudt.

References:
Fender R., et al., 2017, arXiv:1711.04132
Fender R., Gallo E., 2014, Space Sci. Rev., 183, 323
Fender R., et al., 1999, MNRAS, 519, L165
Russell T. D., et al., 2020, MNRAS, 498, 5772