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ATCA radio detection of GX 339-4 in the rising hard state

ATel #5285; James C. A. Miller-Jones (ICRAR - Curtin), Gregory R. Sivakoff (U. Alberta), Tom J. Maccarone (TTU), Adam T. Deller (ASTRON), Peter Jonker (SRON), Gijs Nelemans (U Nijmegen), Tasso Tzioumis (CSIRO), Diego Altamirano (U Amsterdam), Devraj Pawar (U. Mumbai), Dave Russell (IAC, Tenerife)
on 15 Aug 2013; 19:53 UT
Credential Certification: Gregory R Sivakoff (sivakoff@ualberta.ca)

Subjects: Radio, X-ray, Request for Observations, Binary, Black Hole, Transient

Referred to by ATel #: 5594

ATCA radio detection of GX 339-4 in the rising hard state James C.A. Miller-Jones (ICRAR - Curtin), Gregory R. Sivakoff (U. Alberta), Tom J. Maccarone (TTU), Adam T. Deller (ASTRON), Peter Jonker (SRON), Gijs Nelemans (U Nijmegen), Tasso Tzioumis (CSIRO), Diego Altamirano (U Amsterdam), Devraj Pawar (U. Mumbai), Dave Russell (IAC, Tenerife)

Rising optical and near-infrared emission from the black hole X-ray binary GX 339-4 was recently reported to be indicating the early stages of a new outburst (ATel #5244). Following confirmation by Swift of increased X-ray flux indicative of the source being in the low-hard state (ATel #5252), we triggered radio observations of the rising hard state with the Australia Telescope Compact Array (ATCA).

Observations were taken from 08:30-10:30 UT on 2013 August 12 (MJD 56516.40) at central frequencies of 2.1, 5.5, and 9.0 GHz, with 2048 MHz of bandwidth at each frequency. The ATCA was in the relatively compact 750D configuration during the observations.

The data were reduced in CASA, using standard procedures, and owing to the elongated beamshape arising from the snapshot observations, were exported to AIPS for imaging and source extraction. The source was significantly detected at all three frequencies. Image-plane fitting measured flux densities of 3.26±0.28, 3.01±0.09, and 3.59±0.09 mJy beam-1 at 2.1, 5.5, and 9.0 GHz, respectively, suggesting a relatively flat radio spectrum (spectral index α=0.17±0.10, defined as Sν∝να), consistent with a compact jet, as is typically seen in the hard X-ray spectral state.

The closest Swift XRT observation to the ATCA observation (MJD=56516.02) had an unabsorbed X-ray flux in the 3-9 keV energy range of (2.02±0.10) x 10-10 ergs cm-2 s-1 with a photon index of 1.55±-0.10. Thus, the (9 G Hz) radio flux density measurement and (3-9 keV) X-ray flux are entirely consistent with the `universal' FRadio-FX-ray relation for GX 339-4 (Corbel et al. 2013, MNRAS, 428, 2500).

Given the bright radio detection, we have triggered VLBI observations with the Australian Long Baseline Array, which will observe on 2013 August 16th, from 05:15-15:00 UT. We strongly encourage simultaneous multi-wavelength observations at all frequencies.

We thank the ATCA and LBA staff for rapid scheduling of these NAPA observations.

GX 339-4 Outburst Status