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

ATel #4275; P. Romano (INAF-IASF Palermo), H. Krimm (CRESST/GSFC/USRA), T. Sakamoto (GSFC/UMBC), D. N. Burrows (PSU),S. D. Barthelmy (GSFC), M. M. Chester (PSU), P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU), P. Esposito (INAF-IASFMI), P. A. Evans (U Leicester), N. Gehrels (GSFC), V. Mangano (INAF-IASFPA), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU), S. Vercellone (INAF-IASFPA)
on 25 Jul 2012; 14:47 UT
Distributed as an Instant Email Notice Transients
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 2012 July 24 at 04:52:46 (image trigger=528432). Swift immediately slewed to the target, so that the narrow field instruments started observing about 398.9 s after the trigger.

Using the BAT data set from T-239 to T+963 s from the full telemetry downlink, we report that the time-averaged spectrum from T+0 to T+320 s is best fit by a simple power-law model with a photon index of 2.71 +/- 0.85. The fluence in the 15-150 keV band is (2.9+/-1.3)E-07 erg/cm2. All the quoted errors are at the 90% confidence level. The BAT light curve does not show any significant features. The BAT hard X-ray transient monitor does not show significant source activity before or after the trigger interval.

The Swift/XRT light curve reached a count rate in excess of about 10 counts/s. The XRT/PC spectrum (T+409 to T+1192 s, integration time of 783 s) can be fitted with an absorbed power law, with a photon index of 1.0+/-0.4, and an absorbing column density of NH=(3+/-1)E+22 cm-2. The mean flux is ~3E-10 erg/cm2/s (0.3-10 keV, unabsorbed).

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, in press, arXiv:1205.7059), 2012 April 12 (Romano et. al 2012, ATel #4040). The historical light curve from the BAT hard X-ray transient monitor (Krimm et al, 2006, ATel #904; 15-50 keV) can be found at http://swift.gsfc.nasa.gov/docs/swift/results/transients/weak/IGRJ17544-2619 .

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