TITLE: GCN CIRCULAR NUMBER: 19155 SUBJECT: Trigger 677981: Swift detection of IGRJ17091-3624 DATE: 16/03/06 10:18:31 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), H. A. Krimm (CRESST/GSFC/USRA) and K. L. Page (U Leicester) report on behalf of the Swift Team: At 09:41:36 UT, the Swift Burst Alert Telescope (BAT) triggered and located IGRJ17091-3624 (trigger=677981). Swift slewed immediately to the source, although Swift was already looking at this source at the time of the trigger. The BAT on-board calculated location is RA, Dec 257.250, -36.448, which is RA(J2000) = 17h 09m 00s Dec(J2000) = -36d 26' 53" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is typical for image triggers (10 min in this case), there is nothing significant in the real-time light curve. No source was detected in the 2.5-s image taken 676 seconds after the trigger. The X-ray source was, however, bright enough to force the XRT to remain in WT mode. This source is a black hole candidate, which has been reported to be in outburst by Miller et al (ATel #8742) and is being observed as a Swift ToO. The BAT transient monitor shows it to be brightening, reaching ~65 mCrab for the average of 6 March 2016.