TITLE: GCN CIRCULAR NUMBER: 13618 SUBJECT: Swift Trigger 530581: GRB 120811A or a galactic transient DATE: 12/08/11 02:57:33 GMT FROM: Scott Barthelmy at NASA/GSFC B.-B. Zhang (PSU), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 02:35:18 UT, the Swift Burst Alert Telescope (BAT) triggered and located a possible GRB (120811A, trigger=530581). Swift did not slew to the location. The BAT on-board calculated location is RA, Dec 257.183, -22.736 which is RA(J2000) = 17h 08m 44s Dec(J2000) = -22d 44' 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 30 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger. This source was matched to a source 4U 1708-23 (== X Oph X-2) in the on-board catalog, with an offset from the catalog position of 6 arcminutes. However, the latest position available is from the 1972 UHURU catalog, which has a large position uncertainty consistent with this offset. At this time we cannot determine whether this is a GRB, the catalogued 4U 1708-23, or some previously-unknown Galactic transient. Burst Advocate for this burst is B.-B. Zhang (bbzhang AT psu.edu). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)