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New bright outburst of the SFXT IGR J17544-2619 observed by Swift

ATel #6173; P. Romano (INAF-IASFPA), S. D. Barthelmy (GSFC), A. Y. Lien (NASA/CRESST/UMBC), D. N. Burrows (PSU), P. A. Evans (LU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), V. Mangano (PSU), M. H. Siegel (PSU), N. Gehrels (GSFC), P. Esposito (INAF-IASF Milano), S. Vercellone (INAF-IASF Palermo)
on 26 May 2014; 18:06 UT
Credential Certification: Pat Romano (romano@ifc.inaf.it)

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

Referred to by ATel #: 6227, 6566

The Swift Burst Alert Telescope (BAT) triggered on a new outburst from the Supergiant Fast X-ray Transient (SFXT) IGR J17544-2619 on 2014 May 25 at 22:25:47 UT (image triggers=599954 and 599955). Swift immediately slewed to the target, so that the narrow field instruments started observing about 440 s after the trigger.

Using the BAT data set from T-0.0 to T+183 s from the telemetry downlink, we report that the time-averaged spectrum is best-fit by a simple power-law model with a photon index of 3.86+/-0.59. All the quoted errors are at the 90% confidence level.

We note that the source was in outburst when the source came into the BAT FoV during a normal pre-planned slew, and continued to be in outburst past the T+183 s data set interval mentioned above.

The Swift/XRT light curve reached a count rate in excess of 50 counts/s. The XRT/WT spectrum (T+446 to T+1772s, integration 1282 s) can be fit with an absorbed power law, with a photon index of 0.76+/-0.04 and an absorbing column density of NH=2.2(+0.1,-0.1)E+22 cm-2. The mean observed (unabsorbed) flux is about 3.0E-9 (3.5E-9) erg/cm2/s (0.3-10 keV).

Previously, Swift observed bright flares from this source on 2007 November 8 (Krimm et al. 2007, Atel #1265), 2008 March 31 (Sidoli et al. 2009, ApJ, 690, 120), 2008 September 4 (Sidoli et al. 2009, MNRAS, 397, 1528), 2009 March 15 (Krimm et al. 2009, Atel #1971), 2009 June 6 (Romano et al. 2011, MNRAS, 410, 1825), 2010 March 4 (Romano et al. 2011, MNRAS, 412, L30), 2011 March 24 (Farinelli et al. 2012, MNRAS, 424, 2854), 2012 April 12 (Romano et. al. 2012, ATel #4040), 2012 July 24 (Romano et al. 2012, ATel #4275), 2013 June 28 (Romano et al. 2013, ATel #5179), and 2013 September 11 (Romano et al. 2013, ATel #5388). The historical light curve from the BAT hard X-ray transient monitor (Krimm et al, 2013, ApJS, 209, 14; 15-50 keV) can be found at http://swift.gsfc.nasa.gov/docs/swift/results/transients/weak/IGRJ17544-2619 .

BAT Transient Monitor page: IGR J17544-2619