GX 339-4 in transition back to the hard state with the compact jets in formation
ATel #14953; S. Corbel (Universite de Paris), T. Tzioumis (ATNF), L. Tremou (Observatoire de Paris) & F. Carotenuto (Universite de Paris)
on 4 Oct 2021; 13:52 UT
Credential Certification: S. CORBEL (stephane.corbel@cea.fr)
Subjects: Radio, X-ray, Request for Observations, Black Hole
Referred to by ATel #: 15615
GX 339-4 initiated a new outburst earlier this year (see e.g. ATel #14336, #14351, #14352) and the evolution of its X-ray outburst can usually be followed with monitoring such as Swift/BAT and MAXI. GX 339-4 has been in the soft state since 2021, March 28 (ATel #14490, #14507).
The current X-ray light curves (Swift/BAT and MAXI 10-20 keV) indicate that the hard X-ray emission of GX 339-4 has been rising slowly for ~ the last 2 weeks, possibly indicating a transition back to the hard state during the final decay of its 2021 outburst.
We have been monitoring regularly GX 339-4 in radio with the Australia Telescope Compact Array (ATCA), located in Narrabri, Australia. We conducted new radio observations on October 3 and a radio source is detected at the core location with flux density of 0.63 +/- 0.04 mJy at 5.5 GHz and 0.21 +/- 0.4 mJy at 9 GHz. Despite the radio emission is optically thin, we are likely observing the onset and the building up of the compact jets during the decaying hard state (see Corbel et al. 2013, MNRAS, 431, L107). This also likely confirms that GX 339-4 is undergoing a transition back to its final hard state.
Further observations are planned. Multiwavelength support is encouraged in order to follow the spectral evolution.
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.
