Peculiar radio-bright behaviour of the Galactic black hole transient 4U 1543-47 in the 2021-2023 outburst

X. Zhang; W. Yu; F. Carotenuto; S. E. Motta; R. Fender; J. C. A. Miller-Jones; T. D. Russell; A. Bahramian; P. Woudt; A. K. Hughes; G. R. Sivakoff

arXiv · 2501.04917

Peculiar radio-bright behaviour of the Galactic black hole transient 4U 1543-47 in the 2021-2023 outburst

X. Zhang·W. Yu·F. Carotenuto·S. E. Motta·R. Fender·J. C. A. Miller-Jones·T. D. Russell·A. Bahramian·P. Woudt·A. K. Hughes·G. R. Sivakoff

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Abstract

Correlated behaviours between the radio emission and the X-ray emission in Galactic black hole X-ray binaries (BH XRBs) in the X-ray hard state are crucial to the understanding of disc-jet coupling of accreting black holes. The BH transient 4U 1543-47 went into outburst in 2021 following ~19 years of quiescence. We followed it up with ~weekly cadence with MeerKAT for about one year and a half until it faded into quiescence. Multi-epoch quasi-simultaneous MeerKAT and X-ray observations allowed us to trace the compact jet emission and its X-ray emission. In its hard spectral state across three orders of magnitude of X-ray luminosities above ~10$^{34}$ ergs/s, we found the correlation between radio and X-ray emission had a power-law index of 0.82$\pm$0.09, steeper than the canonical value of ~0.6 for BH XRBs. In addition, the radio vs. X-ray correlation shows a large range of the power-law normalization, with the maximum significantly larger than that obtained for most BH XRBs, indicating it can be particularly radio-bright and variable in the X-ray binary sample. The radio emission is unlikely diluted by discrete jet components. The observed peculiar radio-bright and variable behaviours provide the evidence for the relativistic effects of a variable Lorentz factor in the range between 1 and ~2 of the compact jet.

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X. Zhang, W. Yu, F. Carotenuto, S. E. Motta, R. Fender, J. C. A. Miller-Jones, T. D. Russell, A. Bahramian, P. Woudt, A. K. Hughes, G. R. Sivakoff. 2025-01-09. Peculiar radio-bright behaviour of the Galactic black hole transient 4U 1543-47 in the 2021-2023 outburst. https://arxiv.org/abs/2501.04917

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