TITLE: GCN CIRCULAR NUMBER: 5999 SUBJECT: GRB 070107: Swift detection of a burst DATE: 07/01/07 13:10:10 GMT FROM: Scott Barthelmy at NASA/GSFC M. Stamatikos (NASA/ORAU), S.D. Barthelmy (GSFC), M. M. Chester (PSU), G. Cusumano (INAF-IASFPA), W. B. Landsman (NASA/GSFC), T. Mineo (INAF-IASFPA), D. M. Palmer (LANL) and P. Romano (Univ. Bicocca & INAF-OAB) report on behalf of the Swift Team: At 12:05:18 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070107 (trigger=255029). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 159.408, -53.208 which is RA(J2000) = 10h 37m 38s Dec(J2000) = -53d 12' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a broad peak lasting about 40 seconds with smaller structure. The peak count rate was ~2500 counts/sec (15-350 keV), at ~6 sec after the trigger. The XRT began observing the field at 12:08:17.02 UT, 179 seconds after the BAT trigger. XRT did not make an immediate localization. The lightcurve does not show any time variability, however, the spectrum appears consistent with that of a GRB. We are waiting for the full data set from the next Malindi download data pass for futher analysis. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 181 seconds after the BAT trigger, and a finding chart exposure of 400 seconds with the V filter starting 287 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of the BAT error circle, and the 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for extinction.