MeerKAT detects radio emission from 4U 1543-47 that is consistent with a black hole hard state
ATel #15157; Xian Zhang, Wenfei Yu (Shanghai Astronomical Observatory), Rob Fender (University of Oxford), Patrick Woudt (University of Cape Town), James Miller-Jones (Curtin University), Sara Motta (INAF-OAB & University of Oxford), on behalf of the ThunderKAT collaboration
on 11 Jan 2022; 02:00 UT
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)
Subjects: Radio, X-ray, Black Hole, Transient
4U 1543-47, a transient black hole X-ray binary, was found in a new X-ray outburst by MAXI/GSC on June 11, 2021 (ATel #14701). After a probable hard-to-soft spectral state transition on the same day, the source had been residing in the soft spectral state (ATel #14701, #14708, #14725, #14749).
As part of the ThunderKAT Large Survey Programme (Fender et al. 2017, arXiv:1711.04132), which targets on X-ray binaries, Cataclysmic Variables, Supernovae and Gamma-Ray Bursts, we have monitored the black hole transient 4U 1543-47 under the X-ray binary monitoring programme with MeerKAT on ~ weekly cadence since June 19, 8 days after the starting of the X-ray outburst. In each run of the monitoring observations, J1939-6342 was firstly observed, which has been used as the bandpass and absolute flux calibrator. J1501-3918, the phase calibrator, was observed before and after each of the ~ 15 min exposure on 4U 1543-47. Variations in the radio emission from the source were detected (e.g., ATel #14878), but none can be associated with the emission from a compact jet based on X-ray and radio observations.
On January 3, 2022, we detected a radio component with the flux density of 0.24 +/- 0.02 mJy with radio in-band spectral index of 0.28 +/- 0.49. The position of the component is consistent with the Gaia optical position of 4U 1543-47. The hardness ratio obtained with MAXI/GSC (4-10 keV flux over 2-4 keV flux) increased significantly on December 28, 2021. Since then has remained increasing. Based on the radio and X-ray observations, we suggest 4U 1543-47 has transitioned to the hard state and the radio emission is from a compact jet. We encourage multi-wavelength observations to follow up the black hole hard state.
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.
We thank Evangelia Tremou, Joe Bright, Andrew Hughes in the ThunderKAT collaboration for scheduling the observing blocks and the staff at the South African Radio Astronomy Observatory (SARAO) for their rapid scheduling of these observations. The MeerKAT telescope is operated by SARAO, which is a facility of the National Research Foundation, an agency of the Department of Science and Technology. We also thank RIKEN, JAXA and the MAXI team for making the MAXI/GSC data available.
