TITLE:   GCN CIRCULAR
NUMBER:  31202
SUBJECT: GRB 211211A: Swift detection of a bright burst
DATE:    21/12/11 13:32:57 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

A. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA),
V. D'Elia (SSDC & INAF-OAR), J.D. Gropp (PSU), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), T. M. Parsotan (GSFC/UMBC/CRESSTII) and
B. Sbarufatti (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 13:09:59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 211211A (trigger=1088940).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 212.272,  +27.884d which is 
   RA(J2000) = 14h 09m 05s
   Dec(J2000) = +27d 53' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to a telemetry dropout, the immediately
available BAT lightcurve starts at T+8s, and shows a bright complex
burst that extends at least to T+100s.  At T+8s the count rate is 
300k counts/sec (15-350 keV), but the earlier peak may be significantly
higher. 

The XRT began observing the field at 13:11:18.7 UT, 79.2 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 212.2912, 27.8899 which is equivalent to:
   RA(J2000)  = 14h 09m 9.89s
   Dec(J2000) = +27d 53' 23.6"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 64 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 nominal 150.000 seconds with the White
filter starting 87 seconds after the BAT trigger. No credible afterglow
candidate has been found in the initial data products. Data from the 2.7'x2.7'
sub-image are not available at this time. The 8'x8' region for the list of
sources generated on-board covers 100% of the XRT error circle. The list of
sources is typically complete to about 18 mag. No correction has been made for
the expected extinction corresponding to E(B-V) of 0.018. 

Burst Advocate for this burst is A. D'Ai (antonino.dai AT 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/)