[vsnet-grb-info 15589] GRB 141004A: Swift detection of a burst with an optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16878
SUBJECT: GRB 141004A: Swift detection of a burst with an optical counterpart
DATE:    14/10/04 23:29:48 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

V. D'Elia (ASDC), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC),
L. Izzo (URoma/ICRA), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB/PSU) report on behalf
of the Swift Team:

At 23:20:54 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 141004A (trigger=614390).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 76.730, +12.833 which is 
   RA(J2000)  =  05h 06m 55s
   Dec(J2000) = +12d 49' 59"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single FRED
structure with a duration of about 8 sec.  The peak count rate
was ~17000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 23:21:54.2 UT, 59.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 76.73435, 12.81935 which is equivalent
to:
   RA(J2000)  = 05h 06m 56.24s
   Dec(J2000) = +12d 49' 09.7"
with an uncertainty of 4.3 arcseconds (radius, 90% containment). This
location is 51 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.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.14 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 5.3
(+5.50/-4.31) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 64 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	05:06:56.14 =  76.73391
  DEC(J2000) = +12:49:11.3  =  12.81981
with a 90%-confidence error radius of about 0.61 arc sec. This position is 2.3
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.39 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.32. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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.)