TITLE: GCN CIRCULAR NUMBER: 9454 SUBJECT: GRB 090531: Swift detection of a burst DATE: 09/05/31 01:56:55 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), C. Gronwall (PSU), S. T. Holland (CRESST/USRA/GSFC), V. Mangano (INAF-IASFPA) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 01:45:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090531 (trigger=353627). Swift could not immediately slew to the burst location. The BAT on-board calculated location is RA, Dec 178.687, +7.799 which is RA(J2000) = 11h 54m 45s Dec(J2000) = +07d 47' 58" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 50 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~10 sec after the trigger. Because of a Moon constraint, Swift could not slew, and there will be no XRT or UVOT observations until June 3. Burst Advocate for this burst is M. Stamatikos (michael AT milkyway.gsfc.nasa.gov). 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.)