TITLE: GCN CIRCULAR NUMBER: 35411 SUBJECT: GRB 231220A: Swift-XRT follow-up observations DATE: 23/12/21 15:25:45 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), R. Brivio (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the GUANO-detected burst GRB 231220A, collecting 3.6 ks of Photon Counting (PC) mode data between T0+27.0 ks and T0+39.5 ks. No candidate counterpart was detected, with an upper limit of 2.2×10-3 ct s-1 at the best BAT position (GCN 35409). One uncatalogued X-ray source was flagged as spurious after manual inspection. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021638. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/35411. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...