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GCN Circular 14025

GRB 121201A: a GRB with an optical counterpart
2012-12-01T12:47:59Z (12 years ago)
David Palmer at LANL <>
V. N. Yershov (UCL-MSSL), D. N. Burrows (PSU),
N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC),
S. R. Oates (UCL-MSSL), C. Pagani (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and
T. N. Ukwatta (MSU) report on behalf of the Swift Team:

At 12:25:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121201A (trigger=540178).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 13.488, -42.952 which is 
   RA(J2000) = 00h 53m 57s
   Dec(J2000) = -42d 57' 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve is incomplete at this time
due to a telemetry drop out, lacking most of the time period covered
by this image trigger.  Activity is visible starting at T-10s,
but this is coincident with a pre-planned slew. 

The XRT began observing the field at 12:27:37.1 UT, 115.1 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 13.4676,
-42.9432 which is equivalent to:
   RA(J2000)  = 00h 53m 52.22s
   Dec(J2000) = -42d 56' 35.6"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 62 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 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.99 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 1.9
(+1.03/-0.96) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 119 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	00:53:52.17 =  13.46736
  DEC(J2000) = -42:56:34.4  = -42.94290
with a 90%-confidence error radius of about 0.66 arc sec. This position is 3.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.71 with a 1-sigma error of about  0.16. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.01. 

Burst Advocate for this burst is V. N. Yershov (vny AT 
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:
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