TITLE:   GCN CIRCULAR
NUMBER:  14089
SUBJECT: GRB 121217A: Swift detection of a burst
DATE:    12/12/17 07:31:58 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

M. H. Siegel (PSU), B. N. Barlow (PSU), D. N. Burrows (PSU),
M. M. Chester (PSU), V. D'Elia (ASDC), D. Grupe (PSU),
N. P. M. Kuin (UCL-MSSL), C. B. Markwardt (NASA/GSFC),
D. M. Palmer (LANL) and M. Stamatikos (OSU/NASA/GSFC) report on behalf
of the Swift Team:

At 07:17:47 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121217A (trigger=542441).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 153.724, -62.304 which is 
   RA(J2000) = 10h 14m 54s
   Dec(J2000) = -62d 18' 13"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
with some substructure, with a duration of about 60 sec.  The peak count rate
was ~3200 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 07:18:51.8 UT, 64.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 153.70643, -62.35064 which
is equivalent to:
   RA(J2000)  = 10h 14m 49.54s
   Dec(J2000) = -62d 21' 02.3"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 170 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 3.72
x 10^21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.93e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 72 seconds after the BAT trigger. No credible
afterglow candidate has  been found in the initial data products. The
2.7'x2.7' sub-image covers 100% of  the XRT error circle. The 8'x8'
region for the list of sources generated on-board covers 0.00% of the
XRT error circle. Because of the density of catalogued stars,  further
analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the large, but uncertain
extinction  expected. 

Burst Advocate for this burst is M. H. Siegel (siegel AT astro.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/too.html.)