The MeerKAT radio detection of SAX J1808.4-3658 2025 outburst
ATel #17329; Kelebogile Gasealahwe (UCT, SAAO), Rob Fender (Oxford, UCT), Francesco Carotenuto (INAF-OAR) and Andrew Hughes (Oxford) on behalf of the XKAT collaboration
on 12 Aug 2025; 14:50 UT
Credential Certification: Kelebogile Gasealahwe (kelebogilevsb001@gmail.com)
Subjects: Radio, X-ray, Binary, Neutron Star, Transient
Referred to by ATel #: 17369
The Accreting millisecond X-ray Pulsar (AMXP), SAX J1808.4-3658, experiences outbursts every 2-4 years. Following the XB-NEWS report on the 6th August 2025 (Atel #17323) about optical brightening of the source, we triggered radio follow-up with MeerKAT L-band.
On the 7th August 2025 we observed SAX J1808.4-3658 at 1.28 GHz with flux calibrator J1939-6342 and phase calibrator J1830-3602. After a 15 mins long observation starting at 19:07 UTC, the data was imaged using Oxkat (Heywood 2020, 2020ascl.soft09003H). Using PyBDSF methods (Mohan & Rafferty 2015, 2015ascl.soft02007M) we fit the source with an elliptical Gaussian consisting of free parameters and measured a preliminary flux density of 0.50 ± 0.02 mJy/beam.
We will continue to monitor the outburst with MeerKAT and Swift as part of the XKAT collaboration.
We would like to thank the MeerKAT observing staff for the rapid response in scheduling the observation. The MeerKAT telescope is operated by SARAO, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.
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 and Sara Motta. 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.
