TITLE: GCN CIRCULAR NUMBER: 15823 SUBJECT: Trigger 586482: Swift detection of GROJ1744-28 DATE: 14/02/12 17:49:22 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT S. D. Barthelmy (GSFC), J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), S. T. Holland (STScI) and J. A. Kennea (PSU) report on behalf of the Swift Team: At 17:36:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located GROJ1744-28 (trigger=586482). Swift was already on this source from the previous trigger. The BAT on-board calculated location is RA, Dec 266.107, -28.743, which is RA(J2000) = 17h 44m 26s Dec(J2000) = -28d 44' 33" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single FRED-shaped pulse with a duration of about 15 sec. The peak count rate was ~1800 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 17:36:35.0 UT, 27.0 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 266.1382, -28.7407 which is equivalent to: RA(J2000) = +17h 44m 33.17s Dec(J2000) = -28d 44' 26.5" with an uncertainty of 5.2 arcseconds (radius, 90% containment). This location is 98 arcseconds from the BAT onboard position, within the BAT error circle. This position is 1.0 arcseconds from GRO J1744-28. 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 1.92e-09 erg cm^-2 s^-1 (0.2-10 keV). This is the 3rd BAT trigger on GRO J1744-28 in the past 24 hours, the first was reported by Linares et al. (ATEL #5883). The 2nd trigger occurred 17:15:32UT (trigger=586480), which was an image trigger and it is not clear if that trigger was caused by a burst or simply the brightness of the persistent flux. The current trigger is a rate trigger and was caused by a flare. The source is showing rapid bursting activity currently. BAT has triggered on GRO J1744 two previous times since the latest outburst began, on 2014 January 19 20:11UT and 2014 January 23 09:00UT.