GCN Circular 19446

S. D. Barthelmy (GSFC), P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU),
A. Melandri (INAF-OAB), D. M. Palmer (LANL) and T. N. Ukwatta (LANL)
report on behalf of the Swift Team:

At 20:01:47 UT, the Swift Burst Alert Telescope (BAT) triggered on
SGR 1935+2154 (trigger=687123).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 293.750, +21.911, which is 
   RA(J2000)  =  19h 35m 00s
   Dec(J2000) = +21d 54' 39"
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 ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 20:03:08.8 UT, 81.6 seconds after
the BAT trigger. Using promptly downlinked data we find a catalogued
X-ray source located at RA, Dec 293.73150, 21.89454 which is equivalent
to:
   RA(J2000)  = 19h 34m 55.56s
   Dec(J2000) = +21d 53' 40.3"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). 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 1.27
x 10^22 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 85 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 78% of
the XRT 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
XRT 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.