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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
Distributed as an Instant Email Notice Request For Observations
Credential Certification: S. CORBEL (corbel@discovery.saclay.cea.fr)

Subjects: Radio, Infra-Red, Optical, X-ray, Gamma Ray, Request for Observations, Black Hole, Transient

Referred to by ATel #: 2547, 2745, 3191, 3383

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.