TITLE: GCN CIRCULAR NUMBER: 14045 SUBJECT: GRB 121209A: Swift detection of a burst DATE: 12/12/09 22:09:02 GMT FROM: Scott Barthelmy at NASA/GSFC A. Maselli (INAF-IASFPA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU) and E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift Team: At 21:59:11 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 121209A (trigger=540964). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 326.801, -8.244 which is RA(J2000) = 21h 47m 12s Dec(J2000) = -08d 14' 39" 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 60 sec. The peak count rate was ~3300 counts/sec (15-350 keV), at ~20 sec after the trigger. The XRT began observing the field at 22:00:43.3 UT, 92.0 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 326.78917, -8.23262 which is equivalent to: RA(J2000) = 21h 47m 09.40s Dec(J2000) = -08d 13' 57.4" with an uncertainty of 3.9 arcseconds (radius, 90% containment). This location is 58 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (3.81 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.8 (+2.58/-2.19) x 10^21 cm^-2 (90% confidence). UVOT data is not yet available. Burst Advocate for this burst is A. Maselli (maselli 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.)