TITLE: GCN CIRCULAR NUMBER: 19761 SUBJECT: GRB 160804A: Swift detection of a burst DATE: 16/08/04 03:18:08 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT F. E. Marshall (NASA/GSFC), P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), A. Melandri (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 01:32:47 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 160804A (trigger= 707231 ). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 221.639, +10.001 which is RA(J2000) = 14h 46m 33.4s Dec(J2000) = +10d 00m 03.6s with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The XRT began observing the field at 01:35:14 UT, 147 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 221.62909, +9.99599 which is equivalent to: RA(J2000) = 14h 46m 31.0s Dec(J2000) = +09d 59m 45.6s with an uncertainty of 5 arcseconds (radius, 90% containment). This location is 39 arcseconds from the BAT onboard position, within the BAT error circle. Due to bad weather near Guam, we only have limited information about this burst at this time. More information will be available after a full ground station pass. Burst Advocate for this burst is F. E. Marshall (marshall 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.)