TITLE: GCN CIRCULAR NUMBER: 13527 SUBJECT: Trigger 529076: Swift possible detection of SwJ1910.2-0546 DATE: 12/07/29 08:21:55 GMT FROM: Tilan Ukwatta at MSU M. M. Chester (PSU), V. Mangano (INAF-IASFPA), A. Maselli (INAF-IASFPA) and T. N. Ukwatta (MSU) report on behalf of the Swift Team: At 07:13:42 UT, the Swift Burst Alert Telescope (BAT) triggered and located a source (trigger=529076). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 287.652, -5.699 which is RA(J2000) = 19h 10m 37s Dec(J2000) = -05d 41' 54" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peak structure with a duration of about 20 sec. The peak count rate was ~1464 counts/sec (15-350 keV), at ~11 sec after the trigger. The XRT began observing the field at 07:16:01.7 UT, 139.3 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 287.5950, -5.8003 which is equivalent to: RA(J2000) = +19h 10m 22.80s Dec(J2000) = -05d 48' 01.1" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 417 arcseconds from the BAT onboard position and 66 arcseconds from the known source SwJ1910.2-0546. As this position is significantly outside the BAT error circle, it is probably unrelated to the trigger. 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 6.25e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 306 seconds after the BAT trigger. There is a counterpart to the XRT source in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 19:10:22.80 = 287.59499 DEC(J2000) = -05:47:55.8 = -5.79884 with a 90%-confidence error radius of about 0.62 arc sec. This position is 4.2 arc sec. from the center of the XRT error circle. The estimated magnitude is 16.17 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.61.