[vsnet-grb-info 18108] Trigger 701182: Swift detection of SGR 1935+2154

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19556
SUBJECT: Trigger 701182: Swift detection of SGR 1935+2154
DATE:    16/06/23 19:39:26 GMT
FROM:    David Burrows at PSU/Swift  <burrows at astro.psu.edu>

D. N. Burrows (PSU), A. D'Ai (INAF-IASFPA), N. Gehrels (NASA/GSFC),
C. Gronwall (PSU), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC) and
A. Maselli (INAF-IASFPA) report on behalf of the Swift Team:

At 19:24:40 UT, the Swift Burst Alert Telescope (BAT) triggered and
located SGR 1935+2154 (trigger=701182).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 293.716, +21.894 which is 
   RA(J2000) = 19h 34m 52s
   Dec(J2000) = +21d 53' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a short spike
with a duration of about 0.1 sec.  The peak count rate
was ~32000 counts/sec (15-350 keV), at ~0.1 sec after the trigger. 

The XRT began observing the field at 19:25:53.6 UT, 73.8 seconds after
the BAT trigger. Using promptly downlinked data we find an
X-ray source with an enhanced position: RA, Dec 293.7324, 21.8956 which
is equivalent to:
   RA(J2000)  = 19h 34m 55.78s
   Dec(J2000) = +21d 53' 44.0"
with an uncertainty of 3.0 arcseconds (radius, 90% containment). This
position is roughly consistent with SGR 1935+2154.  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 79 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 100% 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.