TITLE: GCN CIRCULAR NUMBER: 31411 SUBJECT: GRB 220107B: Swift-XRT afterglow detection DATE: 22/01/08 09:33:21 GMT FROM: Phil Evans at U of Leicester J. D. Gropp (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), A. Tohuvavohu (U. Toronto) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 220107B (Arimoto et al. GCN Circ. 31409) in a series of observations tiled on the sky. The total exposure time is 1.3 ks, distributed over 2 tiles; the maximum exposure at a single sky location was 1.0 ks. The data were collected between T0+35.7 ks and T0+36.2 ks, and are entirely in Photon Counting (PC) mode. An uncatalogued X-ray source is detected and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 546 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 216.40652, +20.17064 which is equivalent to: RA (J2000): 14h 25m 37.56s Dec(J2000): +20d 10' 14.3" with an uncertainty of 3.4 arcsec (radius, 90% confidence). This position is 11.5 arcmin from the Fermi/LAT position. The source has a mean count rate of 1.3e-01 ct/sec; while we cannot determine at the present time whether it is fading, the fact that the source is well above RASS limit strongly suggests it is the X-ray afterglow of GRB 220107B. More data are currently being collected. The results of the XRT-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/xrt_products/TILED_GRB00103/Source1.php. The results of the full analysis of the tiled XRT observations are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00103. This circular is an official product of the Swift-XRT team.