Swift observations of a new outburst of the SFXT IGR J17544-2619

ATel #5388; P. Romano (INAF-IASFPA), C. B. Markwardt (NASA/GSFC), M. M. Chester (PSU), V. Mangano (PSU), P. A. Evans (U Leicester), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), P. Esposito (INAF-IASFMI), N. Gehrels (GSFC), D. Malesani (DARK/NBI), K. L. Page (U Leicester), S. Vercellone (INAF-IASFPA)
on 12 Sep 2013; 13:20 UT
Credential Certification: Pat Romano (romano@ifc.inaf.it)

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The Swift Burst Alert Telescope (BAT) triggered on a new outburst from the Supergiant Fast X-ray Transient (SFXT) IGR J17544-2619 on 2013 September 11 at 15:59:48 (image trigger=570402). Swift immediately slewed to the target, so that the narrow field instruments started observing about 109 s after the trigger.

Using the BAT data set from T-60 to T+63 s from the telemetry downlink, we report that the time-averaged spectrum from T+0 to T+63 s is best-fit by a simple power-law model with a photon index of 3.27+/-0.29. The fluence in the 15-150 keV band is (3.9+/-0.5)E-7 erg/cm2. All the quoted errors are at the 90% confidence level.

The Swift/XRT light curve reached a count rate of about 40 counts/s and presents several overlapping flares with an overall dynamic range of about 20. The XRT/WT spectrum (T+115 to T+1130 s, integration 1015 s) can be fit with an absorbed power law, with a photon index of 1.0+/-0.1, and an absorbing column density of NH=(3.3+/-0.2)E+22 cm-2. The mean observed (unabsorbed) flux is about 2.0E-9 (2.8E-9) erg/cm2/s (0.3-10 keV). The XRT/PC spectrum (T+1132 to T+7167 s, integration 1394 s) can be fit with an absorbed power law, with a photon index of 1.2+/-0.3, and an absorbing column density of NH=(3.2+/-0.8)E+22 cm-2. The mean observed (unabsorbed) flux is about 3.5E-10 (5.4E-10) 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), and 2013 June 28 (Romano et al. 2012, ATel #5179). The historical light curve from the BAT hard X-ray transient monitor (Krimm et al, 2013, ApJS, in press, arXiv:1309.0755; 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