[vsnet-grb-info 17999] Another Swift detection of SGR 1935+2154 (trigger #687124)

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19447
SUBJECT: Another Swift detection of SGR 1935+2154 (trigger #687124)
DATE:    16/05/21 20:34:22 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU),
A. Melandri (INAF-OAB) and D. M. Palmer (LANL) report on behalf of the
Swift Team:

At 20:23:42 UT, the Swift Burst Alert Telescope (BAT) triggered on
SGR 1935+2154 (trigger=687124) while Swift was observing this source. 
Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 293.730, +21.905, which is 
   RA(J2000)  =  19h 34m 55s
   Dec(J2000) = +21d 54' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike
with a duration less than 0.128 sec.  The peak count rate
was ~9500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 20:24:13.7 UT, 31.7 seconds after
the BAT trigger. No source was detected in 315 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 38 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.