Dipping and flaring in the radio emission from GX 339-4 probably associated with a state transition
ATel #16457; Miriam M Nyamai (SARAO), Lilia Tremou (NRAO), Rob Fender (Oxford) on behalf of the X-KAT team et. al.
on 18 Feb 2024; 15:39 UT
Credential Certification: Evangelia Tremou (etremou@nrao.edu)
Subjects: Radio, Binary, Black Hole, Transient
The recent outburst of GX 339-4, as reported in (ATel #16260) was observed in X-ray and radio wavelengths. NuSTAR observations obtained on 24 January 2024 revealed that the black hole X-ray binary was in hard state during this time (ATel #16425). A day later, on 25 January 2024, the MAXI/GSC detected the system transitioning from hard to soft state (ATel #16424). In a previous update provided in (ATel #16421), we had reported a steady increase in the flux density of GX 339-4 following weekly observations.
After indications that GX 339-4 was likely to transition, we switched to daily monitoring for a duration of two weeks using the MeerKAT telescope. These observations were conducted as part of the X-KAT programme (PI Fender). Subsequently, there was a significant drop in flux density, from 11.5 mJy on 2024-01-22 04:36 UTC, to 3.6 mJy on 2024-01-27 08:08 UTC. Following this decline, the system immediately brightened, reaching a peak of approximately 16 mJy before undergoing further decay. We interpret this behavior as a possible signature of relativistic ejection. Considering the proper motion of GX 339-4 and previous observations of its ejecta, the angular resolution of MeerKAT at S-band observing frequency may be able to resolve ejecta from around the end of March.
Radio monitoring with the MeerKAT is ongoing.
We thank the staff at the South African Radio Astronomy Observatory (SARAO) for scheduling and carrying out these observations. 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.
