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.