[vsnet-grb-info 15918] GRB 141221A: Swift detection of a burst with an optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17206
SUBJECT: GRB 141221A: Swift detection of a burst with an optical counterpart
DATE:    14/12/21 08:21:02 GMT
FROM:    Kim Page at U.of Leicester  <kpa at star.le.ac.uk>

E. Sonbas (NASA/GSFC/Adiyaman Univ.), J. R. Cummings (NASA/UMBC),
V. D'Elia (ASDC), L. Izzo (URoma/ICRA), A. Y. Lien (GSFC/UMBC),
K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB/PSU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 08:07:10 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 141221A (trigger=622006).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 198.269, +8.210 which is 
   RA(J2000) = 13h 13m 05s
   Dec(J2000) = +08d 12' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 20 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 08:08:30.3 UT, 79.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 198.28642, 8.20536 which is equivalent
to:
   RA(J2000)  = 13h 13m 08.74s
   Dec(J2000) = +08d 12' 19.3"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 64 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 in excess of the Galactic value (2.27 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5
(+2.80/-2.41) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 83 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	13:13:08.80 = 198.28666
  DEC(J2000) = +08:12:18.8  =	8.20523
with a 90%-confidence error radius of about 0.61 arc sec. This position is 4.2
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.18 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.03. 

Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.com). 
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.)