GX 339-4 has left the soft state and possibly entered the intermediate state

ATel #7201; Hui Zhang, Wenfei Yu, Wenda Zhang and Zhen Yan (Shanghai Astronomical Observatory, Chinese Academy of Sciences)
on 11 Mar 2015; 07:05 UT
Credential Certification: Hui Zhang (hzhang@shao.ac.cn)

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The black hole transient GX 339-4 started its recent outburst in October 2014 (ATel #6649). It transited from the hard state to the soft state (ATel #6960) and entered the soft state since Jan 21st, 2015 (MJD 57043.03) based on observations with the Swift/XRT (ATel #7009). According to the hardness ratio between the Swift/BAT and MAXI/GSC, the source stayed in the soft state for more than a month from then on. Recently the daily averaged hard X-ray flux detected by Swift/BAT gradually increased from 0.052 +/- 0.004 Crab on MJD 57087.5 to 0.135 +/- 0.008 Crab on MJD 57090.5 in the 15-50 keV band, while the flux in the MAXI/GSC 2-10 keV was almost constant. The hardness ratio between Swift/BAT (15-50 keV) and MAXI/GSC (2-10 keV) has increased from 0.11 +/- 0.02 on MJD 57087.5 to 0.30 +/- 0.02 on MJD 57090.5. According to previous studies (see Yu & Yan 2009, ApJ, 701, 1940; Tang et al. 2011, RAA, 11, 434), the current hardness ratio indicates that the source has left the soft state and probably entered the intermediate state, during which radio jet will start to form. We expect that the source will go back to the hard state in next several days. Multi-wavelength observations are strongly encouraged to study the jet formation in GX 339-4, which has been previously detected by Corbel et al. (2013).