TITLE: GCN CIRCULAR NUMBER: 21283 SUBJECT: GRB 170629A: Swift detection of a burst DATE: 17/06/29 13:22:45 GMT FROM: David Palmer at LANL A. Cholden-Brown (PSU), A. A. Breeveld (UCL-MSSL), S. W. K Emery (UCL-MSSL), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 12:53:33 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 170629A (trigger=759159). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 130.016, -46.587 which is RA(J2000) = 08h 40m 04s Dec(J2000) = -46d 35' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve is incomplete at this time due to lost telemetry, but was still rising at 8 sec after the trigger with a count rate of ~1500 counts/sec. The XRT began observing the field at 12:54:56.0 UT, 82.9 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 129.98653, -46.57155 which is equivalent to: RA(J2000) = 08h 39m 56.77s Dec(J2000) = -46d 34' 17.6" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 91 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. We cannot determine whether the source is fading at the present time. 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 5.16e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 90 seconds with the UVW2 filter starting 86 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. Analysis is complicated because of a nearby bright star (b Vel). Full results will have to await the full dataset. Burst Advocate for this burst is A. Cholden-Brown (aaronb AT swift.psu.edu). 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.)