TITLE: GCN CIRCULAR NUMBER: 6267 SUBJECT: GRB 070411: Swift detection of a burst with optical afterglow DATE: 07/04/11 20:43:42 GMT FROM: Scott Barthelmy at NASA/GSFC A. Moretti (INAF-OAB), S. D. Barthelmy (GSFC), P. J. Brown (PSU), D. N. Burrows (PSU), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC), G. Cusumano (INAF-IASFPA), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/GSFC/USRA), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA), V. Mangano (INAF-IASFPA), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), C. Pagani (PSU), D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB), T. Sakamoto (NASA/ORAU), B. Sbarufatti (INAF-IASFPA), M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester), G. Tagliaferri (INAF-OAB), D. E. Vanden Berk (PSU), S. D. Vergani (DIAS-DCU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 20:12:33 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070411 (trigger=275087). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 107.338, +1.083 which is RA(J2000) = 07h 09m 21s Dec(J2000) = +01d 04' 57" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows an initial weak peak starting at T-1 sec and fading by T+5 sec and then a stronger second peak from T+50 to T+90 sec with an amplitude of ~1000 cnts/sec in the 15-350 keV band. The XRT began observing the field at 20:14:09 UT, 96 seconds after the BAT trigger. XRT found an uncatalogued X-ray source located at RA, Dec 107.3327, +1.0632 which is RA(J2000) = 07h 09m 19.8s Dec(J2000) = 01d 03' 47.5" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 74 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 5.1e-09 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of nominal 100 seconds with the White (160-650 nm) filter starting 244 seconds after the BAT trigger. An afterglow candidate has been found in the initial data products. The 2.7'x2.7' region for the list of sources generated on-board covers 100% of the XRT error circle. A source is detected at RA = 07:09:19.93 Dec = +01:03:52.6 with an estimated uncertainty of +/-0.5 arcsec. The estimated magnitude in the White filter is 18.7. No correction has been made for the large, but uncertain extinction corresponding to a reddening of 0.3 mag.