TITLE: GCN CIRCULAR NUMBER: 43005 SUBJECT: GRB 251205A: Swift detection of a burst with an optical afterglow DATE: 25/12/06 00:02:39 GMT FROM: David Palmer at LANL <palmer@lanl.gov> S. Lanava (PSU), S. Dichiara (PSU), C. Gronwall (PSU), R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 23:39:47 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251205A (trigger=1420873). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 200.243, +29.962 which is RA(J2000) = 13h 20m 58s Dec(J2000) = +29d 57' 45" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 23:42:07.0 UT, 139.8 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 200.2707, 29.9296 which is equivalent to: RA(J2000) = 13h 21m 4.97s Dec(J2000) = +29d 55' 46.6" with an uncertainty of 5.3 arcseconds (radius, 90% containment). This location is 145 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 1.44e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 148 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 13:21:05.34 = 200.27223 DEC(J2000) = +29:55:44.0 = 29.92888 with a 90%-confidence error radius of about 0.75 arc sec. This position is 5.4 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.54 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.014. Burst Advocate for this burst is S. Lanava (sml7284 AT psu.edu). 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/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...