TITLE: GCN CIRCULAR NUMBER: 8080 SUBJECT: GRB 080810: Swift detection of a burst with a bright optical afterglow DATE: 08/08/10 13:31:39 GMT FROM: David Burrows at PSU/Swift K. L. Page (U Leicester), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), P. A. Evans (U Leicester), C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (MSSL), J. Mao (INAF-OAB), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 13:10:12 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080810 (trigger=319584). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 356.779, +0.320 which is RA(J2000) = 23h 47m 07s Dec(J2000) = +00d 19' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multiple-peaked structure with a duration of about 140 sec, including a peak during the time of the XRT/UVOT observations. The peak count rate was ~3000 counts/sec (15-350 keV), at ~22 sec after the trigger. The XRT began observing the field at 13:11:28.3 UT, 76.0 seconds after the BAT trigger. XRT found a bright, flaring, uncatalogued X-ray source located at RA, Dec 356.7936, +0.3188 which is equivalent to: RA(J2000) = 23h 47m 10.4s Dec(J2000) = +00d 19' 07.6" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 52 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of nominal 100 seconds with the White (160-650 nm) filter starting 88 seconds after the BAT trigger. There is a bright candidate afterglow in the list of sources generated on-board at RA(J2000) = 23:47:10.5 = 356.79375 DEC(J2000) = +00:19:10 = +0.31944 with a 1-sigma error radius of about 1.0 arc sec. The estimated white magnitude is 14.7 with a 1-sigma error of about 0.5 mag. No correction has been made for a Galactic extinction corresponding to a reddening of 0.03 mag along the line of sight. We note the presence of the galaxy J234710.47+001906.0 about 1.7 arcsec from the XRT position. Burst Advocate for this burst is K. L. Page (kpa AT star.le.ac.uk). 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.)