MeerKAT detects radio emission from neutron star X-ray binary Aql X-1

ATel #16888; Noa Grollimund (Universite Paris Cite & CEA Saclay), Stephane Corbel (Universite Paris Cite & CEA Saclay & Observatoire de Paris), Rob Fender (Oxford University), Sara Motta (INAF-OAB), on behalf of the X-KAT collaboration
on 30 Oct 2024; 15:45 UT
Distributed as an Instant Email Notice Transients
Credential Certification: S. CORBEL (stephane.corbel@cea.fr)

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The neutron star X-ray binary Aql X-1 entered a new outburst in September 2024 detected by Einstein Probe (ATel #16821) and confirmed at optical and radio wavelengths by LCO (ATel #16822) and the VLA (ATel #16823). SVOM observations suggested that the source transitioned to the X-ray soft state in early October (ATel #16843). Since the beginning of the outburst, we carried out weekly monitoring of the source with MeerKAT, as part of the X-KAT programme. Here, we report on the late-time detection of radio emission from Aql X-1.

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 J2011-0644 for complex gain calibration. Aql X-1 was observed for 15 minutes on 2024-10-26 13:12:31.1 UTC (MJD 60609.55). We detect a radio source at the known position of Aql X-1. Fitting for a point source in the image plane, we measure a flux density of 130 ± 27 uJy. This detection occurs rather late in the outburst, almost one month after our last detection of the source on 2024-09-29. We also note that the radio emission could originate either from discrete ejecta, or from a compact jet.

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.