TITLE: GCN CIRCULAR NUMBER: 16177 SUBJECT: GRB 140428A: Swift Detection of a Possible Burst DATE: 14/04/28 23:34:36 GMT FROM: Scott Barthelmy at NASA/GSFC D. Kocevski (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC), A. Y. Lien (NASA/GSFC/ORAU), D. Malesani (DARK/NBI), C. B. Markwardt (NASA/GSFC) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 22:40:50 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140428A (trigger=597519). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 194.342, +28.357, which is RA(J2000) = 12h 57m 22s Dec(J2000) = +28d 21' 26" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Most of the expected realtime products were not available for this trigger so we have limited information. We know that the trigger duration is 4 seconds and the image significance is 9 sigma during that exposure. A light curve is not yet available. We note that the position reported in TDRSS light curve notices are incorrect. The position reported above is correct. Because of outage in the TDRSS telemetry downlink, all but one BAT light curve notice and all of the XRT notices are missing. Only a pair of UVOT SourceList and Image notices were received on the ground. However, based on the strong detection in BAT, we believe that this is most likely a real GRB. We will issue a Circular when the full dataset is downlinked. Burst Advocate for this burst is D. Kocevski (dankocevski AT gmail.com). 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.)