TITLE: GCN CIRCULAR NUMBER: 6678 SUBJECT: GRB 070729: Swift detection of a short hard burst DATE: 07/07/29 00:48:05 GMT FROM: Scott Barthelmy at NASA/GSFC C. Guidorzi (Univ Bicocca&INAF-OAB), L. M. Barbier (NASA/GSFC), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU), V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), A. Moretti (INAF-OAB), D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 00:25:53 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070729 (trigger=286373). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 56.322, -39.312 which is RA(J2000) = 03h 45m 17s Dec(J2000) = -39d 18' 41" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows three overlapping peaks with a total duration of about 1.5 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began taking data at 00:27:21 UT, 87 seconds after the BAT trigger. The XRT on-board centroid algorithm did not find a source in the image. Using prompt downlinked data, we find an uncatalogued X-ray source located at RA, Dec 56.3147, -39.3234 which is RA(J2000) = 03 45 15.52 Dec(J2000) = -39 19 24.2 with an uncertainty of 5.7 arcsec (radius, 90% containment). This location is 45 arcseconds from the BAT on-board position, within the BAT error circle. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 91 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 18.5 mag. No correction has been made for the expected Galactic extinction corresponding to a reddening of 0.02 mag. Burst Advocate for this burst is C. Guidorzi (cristiano.guidorzi AT brera.inaf.it). 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.)