TITLE: GCN CIRCULAR NUMBER: 6005 SUBJECT: GRB 070110: Swift detection of a burst with a possible optical afterglow DATE: 07/01/10 07:57:12 GMT FROM: Scott Barthelmy at NASA/GSFC H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), M. M. Chester (PSU), G. Cusumano (INAF-IASFPA), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. B. Markwardt (GSFC/UMD), T. Mineo (INAF-IASFPA), K. L. Page (U Leicester), D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB), B. Sbarufatti (INAF-IASFPA), M. Stamatikos (NASA/ORAU) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team: At 07:22:41 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070110 (trigger=255445). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 0.910, -52.961 which is RA(J2000) = 00h 03m 38s Dec(J2000) = -52d 57' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a multi-peaked structure with a duration of about 70 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~18 sec after the trigger. The XRT began observing the field at 07:24:15 UT, 93 seconds after the BAT trigger. XRT found a bright, variable, uncatalogued X-ray source located at RA(J2000) = 00h 03m 39.6s, Dec(J2000) = -52d 58' 29.1", with an estimated uncertainty of 4.2 arcseconds (90% confidence radius). This is a ground calculated position based on prompt downlinked data. This location is 52 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 2.1e-09 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 104 seconds after the BAT trigger. An afterglow candidate is apparent at RA=0.9133 (00h 03m 39.20s), DEC=-52.9740 (-52d 58' 26.3") with an estimated uncertainty of ± 1 arcsec, which is 4.6" from the XRT position. The estimated magnitude is 20.9 (white), with an uncertainty of ± 1 mag. Additional data products are not yet available to confirm the candidate. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.014.