TITLE:   GCN CIRCULAR
NUMBER:  29573
SUBJECT: GRB 210218A: Swift-XRT confirmation of afterglow 
DATE:    21/02/26 16:32:25 GMT
FROM:    Boris Sbarufatti at PSU  <bxs60@psu.edu>

B. Sbarufatti (PSU), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team

Swift-XRT has performed follow up observations of GRB 210218A (Sbarufatti et al. GCN Circ. 29529).
The Swift-BAT trigger happened while the burst position in the sky was Moon constrained for XRT and UVOT observations. 
A first follow up observation was performed when the target emerged from Moon constraint, with one uncatalogued X-ray source (source #3) detected inside the BAT error circle (Sbarufatti et al. GCN Circ. 29542).

Swift-XRT observed the field again, for a further 4.7 ks, from T+497 ks to T+549 ks. Source #3 has faded below detection, with a 3-sigma upper limit of  2.5E-3 cts s^-1 (equivalent to  4.6E-14 erg cm^-2 s^-1 ), and is thus confirmed to be the burst afterglow.

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