TITLE: GCN CIRCULAR NUMBER: 22431 SUBJECT: Swift Trigger 811167: Detection of MAXI J1813-095 DATE: 18/02/22 01:02:05 GMT FROM: David Palmer at LANL 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.