Optical Observations of GX 339-4 in Outburst with the Faulkes Telescope South

ATel #2459; F. Lewis (Faulkes Telescope Project, University of Glamorgan, Open University), D. M. Russell (University of Amsterdam), M. Cadolle Bel (ESA/ESAC, Spain)
on 26 Feb 2010; 17:35 UT
Credential Certification: David M. Russell (D.M.Russell@uva.nl)

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Further to ATel #2455 (see also ATels #2380, #2384) detailing recent INTEGRAL observations of the 2010 outburst of the black hole candidate transient source GX 339-4, we report on our optical monitoring observations: the source has brightened by ~ 4 magnitudes in the last 4 months, since its faint state (ATels #2270, #2281). We note that these are the brightest magnitudes we have measured since we started to monitor the source in September 2007. This is in agreement with the recent reported hard X-ray detections, which also indicate the highest fluxes measured since the bright outburst of 2007.

Our monitoring of the optical counterpart (in Bessel-V, R and SDSS i'-bands; ATels #1586, #1962, #2270) with the Faulkes Telescope South (located at Siding Spring, Australia) shows that GX 339-4 had the following magnitudes: V = 15.9 +/- 0.2, R = 15.2 +/- 0.2 and i' = 15.0 +/- 0.1 between 2010-02-10 and 2010-02-22 UTC (MJD = 55237 - 55249); the errors represent the range of magnitudes measured over these dates. There is no obvious increase or decrease of magnitudes during these dates; the magnitude ranges (differences of ~ 0.4 mag) rather likely represent intrinsic variability of GX 339-4. This is to be expected since this source has proved variable in previous outbursts whilst in the hard state. Our long-term optical light curves are linked below.

According to Wu et al. (2010), this outburst is likely to be bright, peaking at > 0.83 Crab in hard X-rays. This is based on the empirical relationship between peak hard X-ray flux and waiting time since the last bright (> 0.12 Crab) outburst of GX 339-4. The source may therefore make a transition to the soft state in the coming months.

Multi-wavelength observations are therefore encouraged for the following months. The Faulkes Telescope observations are part of an on-going monitoring campaign of ~ 30 low-mass X-ray binaries (Lewis et al. 2008, arXiv:0712.2751). The Faulkes Telescope Project is an educational and research arm of the Las Cumbres Observatory Global Telescope Network (LCOGTN). FL acknowledges support from the Dill Faulkes Educational Trust. DMR acknowledges support from a Netherlands Organisation for Scientific Research (NWO) Veni Fellowship.

GX 339-4 optical light curves