TITLE: GCN CIRCULAR NUMBER: 16477 SUBJECT: GRB 140629A: Swift detection of a burst with an optical counterpart DATE: 14/06/29 14:29:09 GMT FROM: Scott Barthelmy at NASA/GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU) and K. L. Page (U Leicester) report on behalf of the Swift Team: At 14:17:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140629A (trigger=602884). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 248.982, +41.890 which is RA(J2000) = 16h 35m 56s Dec(J2000) = +41d 53' 25" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows an initial rise of the event starting at ~T-5 sec out to ~T+5 sec, at which point there is a gap in the TDRSS light curve so nothing can be said at this time for the light curve past T+5 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 14:19:04.5 UT, 94.2 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 248.97675, 41.87702 which is equivalent to: RA(J2000) = 16h 35m 54.42s Dec(J2000) = +41d 52' 37.3" with an uncertainty of 4.0 arcseconds (radius, 90% containment). This location is 48 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. No spectrum from the promptly downlinked event data is yet available to determine the column density. The initial flux in the 2.5 s image was 6.08e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 101 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 16:35:54.46 = 248.97691 DEC(J2000) = +41:52:36.7 = 41.87685 with a 90%-confidence error radius of about 0.74 arc sec. This position is 0.8 arc sec. from the center of the XRT error circle. The estimated magnitude is 14.81 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.01. Burst Advocate for this burst is A. Y. Lien (yarleen 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.)