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
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
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.