TITLE: GCN CIRCULAR NUMBER: 8182 SUBJECT: GRB 080905B: Swift detection of a burst with possible optical counterpart DATE: 08/09/05 17:22:03 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT M. C. Stroh (PSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), S. Immler (CRESST/GSFC/UMD), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), C. Pagani (PSU), K. L. Page (U Leicester), B. Preger (ASDC), J. L. Racusin (PSU), T. Sakamoto (NASA/UMBC), P. Schady (MSSL-UCL), R. L. C. Starling (U Leicester) and L. Vetere (PSU) report on behalf of the Swift Team: At 16:55:45 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080905B (trigger=323898). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 301.723, -62.571 which is RA(J2000) = 20h 06m 53s Dec(J2000) = -62d 34' 15" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed three well separated peaks each about 10 seconds long with a total burst duration of about 90 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 16:57:28.6 UT, 103.2 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source with an enhanced position: RA, Dec 301.74027, -62.56347 which is equivalent to: RA(J2000) = 20h 06m 57.66s Dec(J2000) = -62d 33' 48.5" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 39 arcseconds from the BAT onboard position, within the BAT error circle. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (3.49e+20 cm^-2, Kalberla et al. 2005), with an excess column of 1.7 (+1.47/-1.31) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 2.11e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 112 seconds after the BAT trigger. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. Inside the XRT error circle is a 16th mag source that is starlike in the DSS, but appears extended or double in the UVOT image and may be an optical afterglow. A second finding chart in V does not allow us to confirm or reject the candidate at this time. No correction has been made for the expected extinction corresponding to E(B-V) of 0.05. Burst Advocate for this burst is M. C. Stroh (stroh AT astroh.org). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)