TITLE: GCN CIRCULAR NUMBER: 16531 SUBJECT: GRB 140706A: Swift detection of a burst with an optical counterpart DATE: 14/07/06 19:42:34 GMT FROM: Scott Barthelmy at NASA/GSFC F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC), J. R. Cummings (NASA/UMBC), J. A. Kennea (PSU), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Swift Team: At 19:33:33 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140706A (trigger=603587). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 49.306, -38.059 which is RA(J2000) = 03h 17m 13s Dec(J2000) = -38d 03' 33" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows two main peaks with a total duration of about 55 sec. The peak count rate was ~1700 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 19:34:46.0 UT, 72.8 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 49.29517, -38.05083 which is equivalent to: RA(J2000) = 03h 17m 10.84s Dec(J2000) = -38d 03' 03.0" with an uncertainty of 4.1 arcseconds (radius, 90% containment). This location is 42 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 5.09e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 82 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 03:17:10.40 = 49.29332 DEC(J2000) = -38:03:07.4 = -38.05205 with a 90%-confidence error radius of about 1.10 arc sec. This position is 4.5 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.05. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02. 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.)