TITLE: GCN CIRCULAR NUMBER: 13619 SUBJECT: Trigger 530588: Swift detection of XMM J174457-2850.3 DATE: 12/08/11 05:10:08 GMT FROM: Scott Barthelmy at NASA/GSFC B. N. Barlow (PSU), S. D. Barthelmy (GSFC), C. Gronwall (PSU), D. M. Palmer (LANL) and B.-B. Zhang (PSU) report on behalf of the Swift Team: At 04:43:53 UT, the Swift Burst Alert Telescope (BAT) triggered and located a burst from the Galactic center region (trigger=530588). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 266.257, -28.852 which is RA(J2000) = 17h 45m 02s Dec(J2000) = -28d 51' 08" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 20 sec. The peak count rate was ~1600 counts/sec (15-350 keV), at ~3 sec after the trigger. The XRT began observing the field at 04:45:02.9 UT, 69.2 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 266.2395, -28.8389 which is equivalent to: RA(J2000) = +17h 44m 57.48s Dec(J2000) = -28d 50' 20.0" with an uncertainty of 4.9 arcseconds (radius, 90% containment). This location is 72 arcseconds from the BAT onboard position, within the BAT error circle. This position is 1.8 arcseconds from that of a known X-ray source: XMM J174457-2850.3, which is known to be currently active. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 4.33e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 234 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18.0 mag. No correction has been made for the large, but uncertain extinction expected.