GCN Circular 14251

D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), C. Gronwall (PSU),
J. A. Kennea (PSU), A. Y. Lien (NASA/GSFC/ORAU),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and
T. N. Ukwatta (MSU) report on behalf of the Swift Team:

At 01:21:40 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a burst from the known position of the Soft Gamma Repeater 
SGR 1806-20 (trigger=549841).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 272.183, -20.393 which is 
   RA(J2000) = 18h 08m 44s
   Dec(J2000) = -20d 23' 33"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peak
structure with a duration of about 0.128 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 01:22:31.6 UT, 50.8 seconds after
the BAT trigger. Using promptly downlinked data we find an X-ray source
with an enhanced position: RA, Dec 272.1635, -20.4104 which is
equivalent to:
   RA(J2000)  = 18h 08m 39.23s
   Dec(J2000) = -20d 24' 37.5"
with an uncertainty of 3.1 arcseconds (radius, 90% containment). This
location is 1.8 arcseconds from that of SGR 1806-20. 

UVOT took a finding chart exposure of 150 seconds with the White 
filter  starting 53 seconds after the BAT trigger.   No optical 
counterpart has  been found in the initial data products.    The 8'x8'
region for the list of sources generated on-board covers  SGR1806-20. 
The list of sources is typically complete to about 18 mag. No  
correction has been made for the large, but uncertain extinction 
expected. 

BAT's most recent detection of a burst from this source was
a month ago (2013-01-20), and a comparably-sized burst was 
most recently detected by BAT on 2010-03-26.