Radio Non-detection of Hercules X-1 during the ALS with MeerKAT/X-KAT

ATel #18042; Teresa Panurach (Naval Research Laboratory), Evangelia Tremou (NRAO), Kristen Dage (Curtin University), Alexandra Tetarenko (University of Lethbridge), Francesco Carotenuto (INAF-OAR), Rob Fender (Oxford & UCT), Sara Motta (INAF) for the X-KAT Collaboration
on 14 Sep 2026; 17:00 UT
Credential Certification: Evangelia Tremou (etremou@nrao.edu)

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Hercules X-1 (Her X-1) is a neutron star X-ray binary with a precessing, warped accretion disk and a 35-day super-orbital period. Since the beginning of 2026, it has been in an anomalous low state (ALS), as indicated by the recently observed suppression of its X-ray emission by a factor of 10 (ATel #17607). Most recent observations of Her X-1 have constrained the first X-ray polarimetric measurement using the Imaging X-ray Polarimetry Explorer (IXPE) during the ALS (Atel #17986).

We report a MeerKAT observation of Her X-1 during the ALS as part of the X-KAT programme. We observed on 2026-08-29 at 14:37UTC at a central frequency of 1.284 GHz (L-band) with a total bandwidth of 860MHz for an on-source integration time of 10 minutes. We did not detect Her X-1 and measured a 3σ upper-limit of 81μJy/beam.

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. We thank the staff at the South African Radio Astronomy Observatory (SARAO) for scheduling and carrying out these observations. For further information on this programme contact Rob Fender or Sara Motta. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory (SARAO), which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.