[vsnet-grb-info 17982] Trigger 686443: Swift detection of SGR 1935+2154

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19430
SUBJECT: Trigger 686443: Swift detection of SGR 1935+2154
DATE:    16/05/16 21:03:29 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
T. G. R. Roegiers (PSU) and T. N. Ukwatta (LANL) report on behalf of
the Swift Team:

At 20:49:46 UT, the Swift Burst Alert Telescope (BAT) triggered and
located SGR 1935+2154  (trigger=686443).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 293.704, +21.880, which is 
   RA(J2000)  =  19h 34m 49s
   Dec(J2000) = +21d 52' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike
structure with a total duration less than 128 msec.  The peak count rate
was ~3600 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 20:51:05.0 UT, 78.1 seconds after
the BAT trigger. No source was detected in 157 s of promptly downlinked
data. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 83 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 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the large, but uncertain extinction expected.