ATCA detects radio emission from the compact jets in Swift J1727.8-1613 following its return to the hard X-ray state
ATel #16552; T. D. Russell (INAF/IASF Palermo), F. Carotenuto (University of Oxford), J. C. A. Miller-Jones (ICRAR/Curtin), P. Atri (Astron), N. Grollimund (Universite Paris Cite/CEA Saclay), S. Corbel (Universite Paris Cite/CEA Saclay/Observatoire de Paris) on behalf of a larger collaboration.
on 22 Mar 2024; 10:37 UT
Credential Certification: Thomas Russell (thomas.russell@inaf.it)
Subjects: Radio, Black Hole, Transient
Referred to by ATel #: 16596
Following the recent report that Swift J1727.8-1613 (GRB 230824A; ATel #16205) was returning to a hard X-ray state (ATel #16541), we triggered radio observations with the Australia Telescope Compact Array (ATCA). Radio data were recorded simultaneously at central frequencies of 5.5GHz and 9GHz, with 2GHz of bandwidth at each frequency. We used PKS B1934-638 for bandpass and flux calibration, and PKS B1730-130 for phase calibration. Data were calibrated and imaged following standard procedures with the Common Astronomy Software Application (CASA, v5.1.2; CASA Team et al. 2022). For imaging, we used a Briggs weighting scheme with a robust parameter of 0, balancing sensitivity and resolution.
Observations taken between 2024-03-21 19:22 UT and 2024-03-22 00:09 UT (MJD 60390.9 +/- 0.1) detected radio emission at the known location of Swift J1727.8-1613 (e.g., ATel #16211). We measured flux densities of 1.21 +/- 0.03 mJy at 5.5GHz and 1.29 +/- 0.03 mJy at 9GHz. These flux densities correspond to a radio spectral index, α, of 0.14 +/- 0.08, where Sν ∝ να. This is consistent with radio emission from a self-absorbed compact jet, typically associated with the hard X-ray state of an X-ray binary.
Further observations are planned. Multiwavelength observations are strongly encouraged.
We thank Jamie Stevens and ATCA staff for making this observation possible. We acknowledge the Gomeroi people as the traditional owners of the ATCA observatory site.
