MeerKAT detection of 4U 1630-47 during its 2026 outburst

ATel #18070; I. Mariani, S. E. Motta (INAF-OAB), R. P. Fender (Oxford University) on behalf of the X-KAT collaboration
on 22 Sep 2026; 12:38 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Sara Elisa Motta (sara.motta@physics.ox.ac.uk)

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The black hole transient 4U 1630-47 started a new outburst on September 2nd, 2026, as observed by SVOM/ECLAIRs (ATel #18030). Follow-up X-ray observations were carried out with NuSTAR starting on Sep 6th, 2026 (ATel #18034), which showed the rise to hard-intermediate state. NuSTAR observations taken on Sep 10th revealed a brighter and softer time-averaged X-ray spectrum compared to the previous observations (ATel #18038).

Following the X-ray detections, we initiated follow-up radio observations with the MeerKAT radio telescope as part of the X-KAT programme. The first 10 minutes observation was carried out on September 13th, 2026, at a central frequency of 1.28 GHz (L-band), with a total bandwidth of 0.85 GHz. J1939-6342 was used for flux and bandpass calibration, J1726-5529 for complex gain calibration. We detected the source at a position RA,DEC (J2000) = 16:34:01.561 +/- 0.008, -47:23:34.71+/- 0.09, consistent with the nominal position of 4U 1630-47, with a preliminary flux density of 4.79 +/-0.14 mJy. The in-band radio spectral index, fitted with a simple power-law, is -0.15 +/- 0.34, consistent with a flat spectrum, typical of a hard-state core jet.

We will continue a weekly monitoring of 4U 1630-47 with the MeerKAT radio telescope. Follow-up multiwavelength observations are encouraged.

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.