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Swift observations of IGR J17544-2619

ATel #1971; H. A. Krimm (CRESST/GSFC/USRA), P. Romano (INAF-IASF Palermo), L. Sidoli (INAF-INAF Milano)
on 16 Mar 2009; 21:48 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

Subjects: X-ray, Binary, Transient

Referred to by ATel #: 2069, 2463, 3235, 4040, 4275, 5179, 5388, 6173, 6566

The Swift/Burst Alert Telescope (BAT) hard X-ray transient monitor detected an outburst from the Supergiant Fast X-ray Transient (SFXT) IGR 17544-2619. The outburst was first seen in a 1024-second exposure starting at 2009-03-15 23:52:40 UT and continued into the next Swift pointing starting at 2009-03-16 01:27:36 UT (1152 sec). The rates in these exposures were, respectively, 0.026 ± 0.005 ct/s/cm^2 (115 mCrab) and 0.032 ± 0.005 ct/s/cm^2 (140 mCrab). The source then faded below detectability before re-brightening twice more on 2009-03-16: to 95 mCrab in a 1152-second exposure beginning 06:16:40 UT and then to 85 mCrab in a 384-second exposure beginning 09:25:52. All BAT rates are measured in the 15-50 keV band.

Swift/XRT data are available from our regular monitoring (Sidoli et al 2008, ApJ, 687, 1230). On 2009-03-14 (01:11:35 to 01:28:56 UT, about 46 hours before the BAT outburst) a 1ks exposure yielded a 3-sigma upper limit at 1.5 X 10^-2 ct/s. A second observation, obtained as a Target of Opportunity, on 2009-03-16 15:35:47 to 17:17:37 UT (2.1ks net exposure, about 16 hours after the outburst), yields a 3-sigma upper limit at 1.3 X 10^-2 ct/s.

We thank Neil Gehrels and the Swift science operations team for approving and scheduling this rapid Target of Opportunity observation.

Swift BAT hard X-ray transient monitor light curves for IGR 17544-2619