TITLE: GCN CIRCULAR NUMBER: 5221 SUBJECT: GRB 060605: Swift detection of a burst with optical counterpart DATE: 06/06/05 18:40:14 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT M. J. Page (UCL-MSSL), A. J. Blustin (UCL-MSSL), P. J. Brown (PSU), O. Godet (U Leicester), S. T. Holland (GSFC/USRA), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA), C. Pagani (PSU), A. M. Parsons (GSFC), G. Sato (GSFC/JSPS/USRA) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift Team: At 18:15:44 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060605 (trigger=213630). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 322.144, -6.060 {21h 28m 35s, -06d 03' 36"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a FRED-like structure with a duration of about 20 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began taking data at 18:17:17 UT, 93 seconds after the BAT trigger. The XRT on-board centroid algorithm did not find a source in the image, however analysis of downlinked PC mode data finds a faint, uncatalogued point source at the following location: RA(J2000): 21h 28m 37.2s Dec(J2000): -06d 03m 35.3s, with an estimated error of 4 arcsec radius (90% containment). This position is 39 arcsec from the center of the BAT error circle and is 4.5 arcsec from the UVOT candidate. UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 98 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 (322.1555,-6.0587) or (21h28m37.32s,-06o03'31.3") with a 1-sigma error radius of about 0.5 arc sec. This position is 41.3 arc sec. from the centre of the BAT error circle. The estimated magnitude is 17.4 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 0.05.