TITLE: GCN CIRCULAR NUMBER: 14057 SUBJECT: GRB 121211A: Swift detection of a burst with an optical counterpart DATE: 12/12/11 14:00:52 GMT FROM: Scott Barthelmy at NASA/GSFC V. Mangano (INAF-IASFPA), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), M. M. Chester (PSU), V. D'Elia (ASDC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), S. T. Holland (STScI), J. A. Kennea (PSU), A. Maselli (INAF-IASFPA), K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), E. Sonbas (NASA/GSFC/Adiyaman Univ.), R. L. C. Starling (U Leicester) and E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift Team: At 13:47:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 121211A (trigger=541200). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 195.544, +30.161 which is RA(J2000) = 13h 02m 11s Dec(J2000) = +30d 09' 40" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows multiple peaks with a total duration of about 180 sec. The peak count rate was ~800 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 13:48:32.3 UT, 89.5 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 195.5332, 30.1489 which is equivalent to: RA(J2000) = +13h 02m 7.97s Dec(J2000) = +30d 08' 56.0" with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 55 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. UVOT took a finding chart exposure of 150 seconds with the White filter starting 96 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 13:02:08.01 = 195.53339 DEC(J2000) = +30:08:54.9 = 30.14858 with a 90%-confidence error radius of about 1.10 arc sec. This position is 1.3 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.49. No correction has been made for the expected extinction corresponding to E(B-V) of 0.01. Burst Advocate for this burst is V. Mangano (vanessa AT ifc.inaf.it). 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.)