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GX 339-4 in transition towards hard states

ATel #3117; T. Munoz-Darias, S. Motta, T. Belloni, H. Stiele (INAF - Brera Observatory)
on 20 Jan 2011; 13:45 UT
Credential Certification: Teo Muñoz-Darias (tmd@brera.inaf.it)

Subjects: X-ray, Binary, Transient

Referred to by ATel #: 3191, 3383, 5252

We report on the last 12 RXTE observations of the black hole transient GX 339-4, which is currently on outburst (ATELs #2380 and #2384). They have been taken after an observing gap of 34 days due to Sun constraints. They show that after a long stay (~8 months) in the high-soft state (see ATELs #2577 and #2593) where the count rate has decreased from ~ 700 to 100 cts/s, the system has started a transition towards hard states. A continuous increase in hardness (PCA channels 7-13 (2.87-5.71 keV)/14-23 (5.71-9.51 keV)) and root mean square amplitude (rms) at constant count rate is observed. We see hardness increasing from 0.12 (29 Dec 2010; 95409-01-45-00) to 0.25 (19 Jan 2011; 96409-01-03-02), and rms from ~3% to 10%. The last observation is consistent with GX 339-4 crossing the soft intermediate state (SIMS) towards the low-hard state (see link below for the current hardness evolution and Munoz-Darias et al. 2011, MNRAS, 410, 679 for rms evolution). Observations at all wavelengths are encouraged.