TITLE: GCN CIRCULAR NUMBER: 7594 SUBJECT: GRB 080413: Swift detection of a burst with an optical afterglow DATE: 08/04/13 03:06:53 GMT FROM: David Palmer at LANL A. P. Beardmore (U Leicester), D. N. Burrows (PSU), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), S. D. Hunsberger (PSU), J. A. Kennea (PSU), C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (NASA/UMBC), M. Stamatikos (NASA/ORAU) and E. Troja (U Leicester/INAF-IASFPA) report on behalf of the Swift Team: At 02:54:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080413 (trigger=309096). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 287.290, -27.679 which is RA(J2000) = 19h 09m 10s Dec(J2000) = -27d 40' 44" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a triple-peaked structure with a duration of about 55 sec. The peak count rate was ~10000 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 02:55:20.0 UT, 60.7 seconds after the BAT trigger. XRT found a bright, fading uncatalogued X-ray source located at RA, Dec 287.2978, -27.6779 which is equivalent to: RA(J2000) = 19h 09m 11.4s Dec(J2000) = -27d 40' 40.4" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 25 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to assess possible redshift constraints using X-ray spectroscopy and the nH-z relation from Grupe et al. (2007). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 76 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 19:09:11.76 = 287.2990 DEC(J2000) = -27:40:40.1 = -27.6778 with a 1-sigma error radius of about 0.6 arc sec. This position is 3.9 arc sec. from the center of the XRT error circle. The estimated magnitude is 15.2 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 0.16.