Bright outburst of the SFXT IGR J17544-2619 observed by Swift

ATel #6566; P. Romano (INAF-IASFPA), S. D. Barthelmy (GSFC), V. Mangano (PSU), M. H. Siegel (PSU), P. A. Evans (U. Leicester), D. N. Burrows (PSU), S. Campana (INAF-OAB), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU), N. Gehrels (GSFC), P. Esposito (INAF-IASF Milano), S. Vercellone (INAF-IASF Palermo)
on 11 Oct 2014; 14:41 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 2014 Oct 10 at 15:04:19 UT (image trigger=614903). Swift immediately slewed to the target, so that the narrow field instruments started observing about 132 s after the trigger.

The mask-weighted light curve shows the source was detected as soon as it came into the BAT FOV at T-104 s. It shows an increase around T0, after which was more or less constant until it went out of the FOV due to a constraint slew at T+500 sec. The time-averaged spectrum from T-8.8 to T+493s is reasonably fit by an OTTB model with a kT=9.21+/-0.50 keV. The quoted errors are at the 90% confidence level.

We find a refined XRT position of RA, Dec = 268.60545, -26.33144, equivalent to:
RA(J2000) = 17h 54m 25.31s
Dec(J2000) =-26d 19' 53.2''
with an uncertainty of 1.4 arcseconds (radius, 90% containment). The Swift/XRT WT spectrum (T+136 to T+306s) can be fit with an absorbed power law, with a photon index of 0.70(+0.07,-0.07) and an absorbing column density of NH=1.29(+0.10,-0.09)E+22 cm-2. The mean observed (unabsorbed) flux is about 2.7E-8 (3.2E-8) erg/cm2/s (0.3-10 keV).

The Swift/UVOT detected the known optical source in the optical, uvw1 and uvw2 passbands. The measured photometry is consistent with measures from previous triggers and shows no significant variation over the course of the observations.

Previously, Swift reported 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), 2013 September 11 (Romano et al. 2013, ATel #5388), and 2014 May 25 (Romano et al. Atel #6173). 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