TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5544 SUBJECT: GRB 060908: Swift detection of a burst with a bright optical counterpart DATE: 06/09/08 09:16:22 GMT FROM: Scott Barthelmy at NASA/GSFC P. A. Evans (U Leicester), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), O. Godet (U Leicester), C. Guidorzi (Univ Bicocca&INAF-OAB), J. A. Kennea (PSU), A. N. Morgan (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), P. Romano (INAF-OAB), G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 08:57:22 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060908 (trigger=228581). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 31.835, +0.370 {02h 07m 20s, +00d 22' 14"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows 3 overlapping peaks starting at ~T-10 sec and then a 4th peak lasting until T+12 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~T+2 sec after the trigger. The XRT began observing the field at 08:58:34 UT, 72 seconds after the BAT trigger. XRT found a fading and uncatalogued X-ray source located at RA(J2000) = 02h 07m 18.1s, Dec(J2000) = +00d 20' 29.1", with an estimated uncertainty of 3.8 arcseconds (90% confidence radius). This location is 108 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 5.0e-10 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 80 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at (RA,DEC) (J2000) of (31.8265,0.3420) or (02h07m18.36s,+00o20'31.2") with a 1-sigma error radius of about 0.7 arc sec. This position is 3.8 arc sec. from the center of the XRT error circle. The estimated magnitude is 15.1 with a 1-sigma error of about 0.5 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.03.