GCN Circular 19135
S. D. Barthelmy (GSFC) and K. L. Page (U Leicester) report on behalf of the Swift Team: At 22:40:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located IGR17091-3624 (trigger=677582). Swift was already observing this source. The BAT on-board calculated location is RA, Dec 257.217, -36.401, which is RA(J2000) = 17h 08m 52s Dec(J2000) = -36d 24' 02" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is typical for image triggers (6 min in this case), the light curve does not show anything significant except for two brief peaks (each ~10 sec long) separated by ~450 sec. These peaks could easily be due to a noisy detector. We will not be able to say until the full data has been downloaded and a mask-weight light curve generated. The peak count rate was ~300 counts/sec (15-350 keV). No source was detected in the 2.5-s promptly available image, taken 434.s seconds after the BAT trigger. We are waiting for the full dataset to detect and localise the XRT counterpart. UVOT took a finding chart exposure of 150 seconds with the White filter starting 438 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 25% of the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain extinction expected.