TITLE: GCN CIRCULAR NUMBER: 5691 SUBJECT: GRB 061004: Swift detection of a burst DATE: 06/10/04 20:12:10 GMT FROM: David Palmer at LANL H. Ziaeepour (UCL-MSSL), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), S. R. Oates (UCL-MSSL), C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 19:50:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 061004 (trigger=232339). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 97.748, -45.894 {06h 30m 60s, -45d 53' 36"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a peak with a duration of about 6 sec. The peak count rate was ~5000 counts/sec (15-350 keV), at ~3 sec after the trigger. The XRT began observing the field at 19:51:30 UT, 60 seconds after the BAT trigger. XRT found a bright, variable, uncatalogued X-ray source located at RA(J2000) = 06h 31m 10.52s, Dec(J2000) = -45d 54' 24.0", with an estimated uncertainty of 6 arcseconds (90% confidence radius). This location is 124 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 4.6e-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 69 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 18.0 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.049