MeerKAT detection of a radio flare from black hole X-ray binary V4641 Sgr
ATel #16852; Noa Grollimund (Universite Paris Cite & CEA Saclay), Stephane Corbel (Universite Paris Cite & CEA Saclay & Observatoire de Paris), Rob Fender (Oxford University), on behalf of the X-KAT collaboration
on 8 Oct 2024; 08:30 UT
Credential Certification: S. CORBEL (stephane.corbel@cea.fr)
Subjects: Radio, X-ray, Request for Observations, Black Hole, Transient
Referred to by ATel #: 16916
The black hole X-ray binary V4641 Sgr recently began an outburst, detected by MAXI/GSC (ATel #16804) and confirmed by INTEGRAL/JEM-X (ATel #16811), Swift/XRT and MeerKAT (Atel #16819). Since then, we carried out weekly monitoring of the source with MeerKAT, as part of the X-KAT programme. Here, we report on the detection of a radio flare from V4641 Sgr.
Radio observations were carried out at a central frequency of 1.28 GHz, with a total bandwidth of 860 MHz. We used J1939-6342 for flux and bandpass calibration, and J1833-2103 for complex gain calibration. V4641 Sgr was observed for 15 minutes on 2024-09-29 12:57:36 UTC (MJD 60582.547 ± 0.005) and on 2024-10-06 12:28:48 UTC (MJD 60589.527 ± 0.005). On 2024-09-29, i.e. ~ two weeks after the initial MeerKAT detection (Atel #16819), the source was not detected anymore (3-sigma upper limit of ~87 uJy/beam). On 2024-10-06, we detected a radio source at the known position of V4641 Sgr. Fitting for a point source in the image plane, we measure a flux density of 15.5 ± 0.1 mJy. A preliminary analysis of these observations suggests that the source is undergoing a radio flare, or at least is showing enhanced radio emission.
Multi-wavelength observations are encouraged to study the evolution of the outburst. Further radio monitoring is planned, as well as weekly Swift observations of the target.
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.
