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ATEL # 1019; Turler M. (ISDC, Geneva), Balman S., Bazzano A., Beckmann V., Belloni T., Boggs S., Capitanio F., Chenevez J., Del Santo M., Diehl R., Donnarumma I., Eckert D., Goldoni P., Gotz D., Leyder J.-C., Mereghetti S., Paizis A., Pottschmidt K., Sidoli L., Tarana A., Tueller J., Walter R., Watanabe K., Weidenspointner G.
on 3 Mar 2007; 16:06 UT
Password Certification: Nami Mowlavi (Nami.Mowlavi@obs.unige.ch)
Subjects: X-ray, Gamma Ray, Binaries, Neutron Stars, Transients
During the INTEGRAL Key Programme observations of the galactic bulge region on March 2, 2007, the IBIS/ISGRI instrument observed a bright outburst from the supergiant fast X-ray transient XTE J1739-302 = IGR J17391-3021. The source is thought to be a high-mass X-ray binary with a neutron star and is known to produce short X-ray outbursts. The first detection by INTEGRAL was reported by Sunyaev et al. (2003, ATel #181) and several other such events are described by Sguera et al. (2006, ApJ 646, 452), but this one is among the brightest.
Timing analysis of the event in time bins of 400 seconds reveals a structured lightcurve starting on March 2, 2007 at about 13:30 UT, reaching a maximum after an hour and fading over 0.5 to 1 hour. The exact duration of the outburst is unknown due to a half-hour telemetry loss at the end of the event. The maximum flux reached is of about 330 mCrab in the 20-40 keV band and 250 mCrab in the 40-80 keV band. There was no other strong activity of the source within several hours before and after the outburst.
We extracted a spectrum of the source in the science window lasting 2741 seconds during which the source was the brightest. The resulting spectrum in the 20-100 keV range (the outburst occurred outside the JEM-X field of view) can be satisfactorily fitted by either a thermal bremmstrahlung model or a cut-off powerlaw, but not by a single powerlaw or a blackbody model. The best bremmstrahlung model fit has a temperature of kT = 22.5 +/- 1.3 keV.
Lightcurve of the outburst