GCN Circular 22431

A. P. Beardmore (U Leicester), D. N. Burrows (PSU), A. Deich (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), H. A. Krimm (NSF/USRA),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 00:20:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located MAXI J1813-095 (trigger=811167; ATel #11323 Kawase et al). 
Swift slewed to the location immediately after the 26 minute
image exposure was complete.  The BAT on-board 
calculated location is 
RA, Dec 273.387, -9.501 which is 
   RA(J2000) = 18h 13m 33s
   Dec(J2000) = -09d 30' 02"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). 

The XRT began observing the field at 00:51:25.7 UT, 1858.3 seconds
after the BAT trigger. XRT found a bright X-ray source
located at RA, Dec 273.3916, -9.5305 which is equivalent to:
   RA(J2000)  = +18h 13m 33.98s
   Dec(J2000) = -09d 31' 49.8"
with an uncertainty of 5.7 arcseconds (radius, 90% containment). This
location is 107 arcseconds from the BAT onboard position, within the
BAT error circle, and 8.9 arcseconds from the known transient MAXI 
J1813-095 (Kennea et al., ATel #11326) No event data are yet available
to determine the column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 9.25e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 104 seconds with the White filter
starting 1867 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. 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.