TITLE: GCN CIRCULAR NUMBER: 35410 SUBJECT: GRB 231220A: Swift ToO observations DATE: 23/12/20 23:38:36 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a ToO observation of the GUANO GRB 231220A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021638

Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the GUANO event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

This circular is an official product of the Swift-XRT team.

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