TITLE:   GCN CIRCULAR
NUMBER:  15760
SUBJECT: GRB 140129A: Swift detection of a burst with an optical afterglow
DATE:    14/01/29 03:35:31 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

A. Melandri (INAF-OAB), W. H. Baumgartner (GSFC/UMBC),
M. G. Bernardini (INAF-OAB), N. Gehrels (NASA/GSFC),
J. A. Kennea (PSU), A. Y. Lien (NASA/GSFC/ORAU),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/PSU), C. A. Swenson (PSU) and
T. N. Ukwatta (MSU) report on behalf of the Swift Team:

At 03:23:59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 140129A (trigger=585128).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 37.869, -1.587 which is 
   RA(J2000) = 02h 31m 29s
   Dec(J2000) = -01d 35' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peaked
structure with a duration of about 5 sec.  The peak count rate
was ~500 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 03:25:52.9 UT, 113.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 37.89128, -1.59554 which
is equivalent to:
   RA(J2000)  = 02h 31m 33.91s
   Dec(J2000) = -01d 35' 43.9"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 85 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 (2.55 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.2
(+1.80/-1.58) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 116 seconds after the BAT trigger. There is a candidate afterglow in
the list of sources generated on-board at
  RA(J2000)  =	02:31:33.81 =  37.89087
  DEC(J2000) = -01:35:43.3  =  -1.59536
with a 90%-confidence error radius of about 1.10 arc sec. This position is 1.6
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.74. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.03. 

Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.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.)