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GX 339-4 in transition from the hard state

ATel #2545; S. Motta, T. Belloni, T. Muñoz Darias (INAF - Brera Observatory)
on 10 Apr 2010; 11:06 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Tomaso Belloni (belloni@merate.mi.astro.it)

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

Referred to by ATel #: 2547, 2556, 2573, 3191, 3383

The latest RXTE/PCA observation of the black-hole candidate GX 339-4 (2010 April 10, 05:56UT) shows clear evidence that the source is leaving the low-hard state. The power-density spectrum is dominated by two broad-band components with characteristic frequencies around 1 Hz and 9 Hz, on which a narrow QPO with centroid 1.1 Hz is visible. Both components are consistent with the evolution at higher frequencies of features observed previously in the hard state (see Atel 2523). The fractional integrated rms is 24% (0.1-64 Hz). A preliminary fit to the PCA energy spectrum with a power law, a disk blackbody and a Gaussian emission line (with interstellar absorption) yields a power law photon index of 1.7 and a disk inner temperature of ~1 keV. The disk component is required by the fit. Considerable softening is expected in the next few days, based on previous outbursts. In particular, the radio emission is expected to evolve and lead to a major ejection, also considering the relative brightness of the outburst. Multiwavelength observations covering this transition are encouraged.

Light curve and hardness-intensity diagram for the current GX 339-4 outburst