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GCN Circular 14057

Subject
GRB 121211A: Swift detection of a burst with an optical counterpart
Date
2012-12-11T14:00:52Z (11 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
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.)
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