GCN Circular 28879

J.D. Gropp (PSU), N. J. Klingler (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC) and K. L. Page (U Leicester) report on
behalf of the Neil Gehrels Swift Observatory Team:

At 09:45:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located SGR 1830-0645 (trigger=1005428).  Swift slewed immediately to 
the source. The BAT on-board calculated location is 
RA, Dec 277.701, -6.741 which is 
   RA(J2000) = 18h 30m 48s
   Dec(J2000) = -06d 44' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a very short duration. The peak count rate
was ~6480 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 09:45:57.7 UT, 51.5 seconds after
the BAT trigger. Using promptly downlinked data we find an 
X-ray source with an enhanced position: RA, Dec 277.6736, -6.7548 which
is equivalent to:
   RA(J2000)  = 18h 30m 41.66s
   Dec(J2000) = -06d 45' 17.2"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 109 arcseconds from the BAT onboard position, within the
BAT error circle, and consistent with the known location of SGR 1830-0645. 
This position may be improved as more data are received; the latest position 
is available at https://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 (1.11 x
10^22 cm^-2, Willingale et al. 2013), with an excess column of 1.1
(+0.80/-0.68) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 55 seconds after the BAT trigger. No credible counterpart has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any counterpar in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the XRT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any counterpart in the
region. 

Swift first triggered on SGR 1830-0645 on 2020 October 10 (GCN Circ. 
28594
Not found
 
 
), although a sub-threshold flare was also detected on October 05
(GCN 28603
Not found
 
 
).   The source again triggered Swift-BAT on November 05
(GCN Circ. 28838
Not found
 
 
).