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Flaring activity and cyclotron line in GX 304-1 observed with INTEGRAL

ATel #3902; D. Klochkov, A. Santangelo, R. Staubert, V. Doroshenko, G. Puehlhofer (IAAT), C. Ferrigno, E. Bozzo, C. Tchernin (ISDC), I. Caballero (CEA Saclay), P. Kretschmar (ESA), I. Kreykenbohm, J. Wilms (Univ. Erlangen-Nuernberg), K. Pottschmidt (CRESST-UMBC/NASA-GSFC), R. E. Rothschild (UCSD), C. A. Wilson-Hodge (NASA-MSFC), V. McBride (SAAO/UCT), G. Schoenherr (AIP)
on 1 Feb 2012; 11:43 UT
Credential Certification: Dmitry Klochkov (klochkov@astro.uni-tuebingen.de)

Subjects: X-ray, Binary

The INTEGRAL monitoring of the on-going outburst of the transient accreting pulsar GX 304-1 with a Be optical companion revealed strong flaring activity with X-ray flux variations by a factor of ~2 on a time scale of ~1 hour (18-80 keV). The INTEGRAL observations started around MJD 55943. The maximum flux level measured by ISGRI so far is 964 +/- 2 mCrab in the 20-40 keV range. The cyclotron resonance scattering feature is present in the ISGRI and SPI spectra of the source. In the ISGRI data taken around MJD ~55944, it can be modeled with a Gaussian absorption line with a best fit centroid energy of 52.4 +/-1.3 keV and a width (sigma) of 6+/-1 keV. Due to the possibility that the observations are affected by solar flares, the actual line position might be subject to systematic uncertainties at the level of a few keV. The detailed spectral study is ongoing. We thank the INTEGRAL team for the effective communication and prompt scheduling of the TOO observations.