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GCN Circular 19590

Subject
Trigger 701590: Swift detection of a bright outburst from SGR 1935+2154
Date
2016-06-26T14:12:09Z (8 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), N. Gehrels (NASA/GSFC),
C. Gronwall (PSU) and D. M. Palmer (LANL) report on behalf of the
Swift Team:

At 13:54:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located SGR 1935+2154 (trigger=701590).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 293.730, +21.884 which is 
   RA(J2000)  =  19h 34m 55s
   Dec(J2000) = +21d 53' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike
with a duration of about 0.3 sec.  The peak count rate
was ~416,000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 13:56:19.8 UT, 108.9 seconds after
the BAT trigger. Using promptly downlinked data we find a
X-ray source located at RA, Dec 293.73009, 21.89586 which is equivalent
to:
   RA(J2000)  = 19h 34m 55.22s
   Dec(J2000) = +21d 53' 45.1"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This is
consistent with the known source 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 in excess of the Galactic value (1.27 x
10^22 cm^-2, Willingale et al. 2013), with an excess column of 6
(+6.83/-4.97) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 112 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.
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