TITLE: GCN CIRCULAR NUMBER: 16904 SUBJECT: Trigger 614903: Swift detection of IGR J17544-2619 DATE: 14/10/10 15:38:21 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), M. G. Bernardini (INAF-OAB), D. N. Burrows (PSU), P. D'Avanzo (INAF-OAB), D. Malesani (DARK/NBI), V. Mangano (PSU), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), P. Romano (INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU) and T. N. Ukwatta (LANL) report on behalf of the Swift Team: At 15:04:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located a transient (trigger=614903). Swift slewed immediately to the transient. The BAT on-board calculated location is RA, Dec 268.607, -26.330 which is RA(J2000) = 17h 54m 26s Dec(J2000) = -26d 19' 48" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is an image trigger so details of the lightcurve can not yet be determined. The XRT began observing the field at 15:06:31.7 UT, 132.4 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 268.6054, -26.3282 which is equivalent to: RA(J2000) = +17h 54m 25.30s Dec(J2000) = -26d 19' 41.5" with an uncertainty of 5.8 arcseconds (radius, 90% containment). This location is 8.3 arcseconds from the BAT onboard position, within the BAT error circle. This position is 11.1 arcseconds from that of the Supergiant Fast X-ray Transient IGR J17544-2619, which is likely to be the transient that triggered the BAT. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 0.1 s image was 2.08e-08 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 168 seconds with the U filter starting 138 seconds after the BAT trigger. The 2.7'x2.7' sub-image reveals the known optical counterpart at a U magnitude of 15.27 approximately 10.6" from the XRT source. No other source is detected to a typical 3-sigma upper limit of about 19.2 mag. No correction has been made for the large, but uncertain extinction expected.