TITLE: GCN CIRCULAR NUMBER: 25473 SUBJECT: GRB 190816A: Swift-XRT afterglow detection DATE: 19/08/25 04:57:43 GMT FROM: Kim Page at U.of Leicester A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), A. Tohuvavohu (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has conducted further observations of the field of the Swift/BAT-detected burst GRB 190816A (Ukwatta et al. GCN Circ. 25405). The observations now extend from T0+141.7 ks to T0+723.4 ks. The source previously reported by D'Ai et al. (GCN Circ. 25399), "Source 4", is fading with 3-sigma significance, and is therefore likely the GRB afterglow. Using 267 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 = 341.18949, -29.75761 which is equivalent to: RA (J2000): 22h 44m 45.48s Dec(J2000): -29d 45' 27.4" with an uncertainty of 4.9 arcsec (radius, 90% confidence). This position is 64 arcsec from the Swift/BAT position. The source is fading with alpha >0.5. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00920783. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00920783. This circular is an official product of the Swift-XRT team.