TITLE:   GCN CIRCULAR
NUMBER:  15516
SUBJECT: GRB 131127A: Swift detection of a burst
DATE:    13/11/27 10:33:41 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

C. B. Markwardt (NASA/GSFC), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC), V. D'Elia (ASDC), D. Malesani (DARK/NBI),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and P. Romano (INAF-IASFPA) report on behalf of
the Swift Team:

At 10:11:35 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131127A (trigger=579571).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 332.751, +36.590 which is 
   RA(J2000)  =  22h 11m 00s
   Dec(J2000) = +36d 35' 24"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several overlapping
peaks with a duration of about 50 sec.  The peak count rate
was ~1600 counts/sec (15-350 keV), at 0 sec after the trigger. 

The XRT began observing the field at 10:13:09.3 UT, 93.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
332.7293, 36.6098 which is equivalent to:
   RA(J2000)  = 22h 10m 55.03s
   Dec(J2000) = +36d 36' 35.2"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 94 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 1.15
x 10^21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.33e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 102 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 typical 3-sigma upper limit has been about 19.6 mag. 
Data from the list of sources generated on-board are not available at this
time. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.14. 

Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt AT nasa.gov). 
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.)