Observations with the ATCA of the brightest known radio hard state in GX 339-4
ATel #2525; S. Corbel (Univ. Paris Diderot & CEA Saclay), J. Broderick (Univ. Southampton), C. Brocksopp (MSSL), T. Tzioumis (ATNF), R. Fender (Univ. Southampton).
on 30 Mar 2010; 12:33 UT
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Subjects: Radio, Infra-Red, Optical, X-ray, Gamma Ray, Request for Observations, Black Hole, Transient
The recurrent black hole candidate GX 339-4 has entered a new outburst early this year (ATel #2380). It has continuously
been observed in the hard state (ATel #2384, #2455, #2459), that is typically observed in the rising part of the outburst.
Since its reactivation, we have been monitoring GX 339-4 very frequently in radio with the Australia Telescope
Compact Array and the new CABB back-end (mostly at 5.5 GHz and 9 GHz). The last observations conducted on
2010 March 28 show flux densities of the order of 20 mJy with an inverted radio spectrum (spectral index in the
range: +0.1 to +0.2), typical of the powerful self-absorbed compact jets observed in the hard state. This is the
brightest level of radio emission ever found for GX 339-4 in the hard state (e.g. Corbel et al. 2003, A&A, 400, 1007) and
possibly also for any black hole in the hard state.
As GX 339-4 may continue to rise in the hard state for a while (Wu et al. 2019, A&A, 512, 32, but see also ATel #2523 ),
it should also continue to rise at radio frequencies. Further multi-wavelength observations, with X-ray, optical and
infrared observations (including high time resolution observations), are strongly encouraged in order to probe the
contributions of jets at all wavelengths in black holes.