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INTEGRAL observes an increasing Hard X-ray flux of GX 339-4

ATel #2455; L. Prat (CEA Saclay, France), M. Cadolle Bel (ESA/ESAC, Spain), R. Terrier (CNRS/APC, France), L. Pavan, I. Vovk (ISDC, Switzerland), J. Rodriguez, S. Corbel, M. Coriat (CEA Saclay, France), E. Kuulkers (ESA/ESAC, Spain), on behalf of the INTEGRAL Galactic bulge monitoring team
on 24 Feb 2010; 15:52 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Lionel Prat (lionel.prat@cea.fr)

Subjects: X-ray, Gamma Ray, Binary, Black Hole, Transient

Referred to by ATel #: 2459, 2525, 2573, 3191, 3383

Since the beginning of 2010, GX 339-4 entered a new outburst phase (ATEL #2380, #2384). INTEGRAL observed the source between Feb. 10th and Feb. 22th, during the Galactic Bulge and the RX J1713.7-3946 programs. These observations correspond to a total of 850ks exposure time.

Between February 13th and 16th, GX 339-4 displayed a steady count rate of 25-30 cts/s in the 20-40 keV ISGRI energy band (~160-200 mCrab). A simple power law fit to the data yields to a photon index of 1.86 +/- 0.02. At this time, its flux was:

18-40 keV: 1.51 e-09 ergs/cm^2/s
40-80 keV: 1.45 e-09 ergs/cm^2/s
80-150 keV: 1.44 e-09 ergs/cm^2/s

At the end of these observations, between Feb. 19th and Feb. 22th, the 20-40 keV ISGRI flux of GX 339-4 has increased to above ~200 mCrab. A power law fit gives a photon index of 1.89 +/- 0.02. At this time, its flux was:

18-40 keV: 1.63 e-09 ergs/cm^2/s
40-80 keV: 1.53 e-09 ergs/cm^2/s
80-150 keV: 1.49 e-09 ergs/cm^2/s

Between Feb. 10th and Feb. 22th, the Hard X-ray flux of GX 339-4 has thus slowly increased, while the source stayed in the Hard State. This behavior is consistent with the Swift/BAT lightcurve, which shows an increase in the flux since Feb. 19th, after a few days-long plateau. The hard X-ray flux of GX 339-4 is now higher than during every minor outbursts since the major one of 2007, and still increasing. Multiwavelength follow-ups of the source are strongly encouraged.

We thank ISDC for providing the results of their quick look analysis.