GCN Circular 28838

J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), M. J. Moss (GWU),
D. M. Palmer (LANL) and B. Sbarufatti (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 02:22:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located SGR 1830-0645 (trigger=1004219).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 277.679, -6.754 which is 
   RA(J2000) = 18h 30m 43s
   Dec(J2000) = -06d 45' 13"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of <~ 0.1 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 02:23:38.0 UT, 94.8 seconds after
the BAT trigger. Using promptly downlinked data we find a X-ray source 
with an enhanced position: RA, Dec 277.6736, -6.7550 which is 
equivalent to:
   RA(J2000)  = 18h 30m 41.67s
   Dec(J2000) = -06d 45' 17.9"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 19 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at https://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. 

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 2
(+2.39/-1.60) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 97 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 counterpart 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. No correction has been made for the large, but uncertain, extinction
expected.