TITLE:   GCN CIRCULAR
NUMBER:  29892
SUBJECT: GRB 210421B: Swift-XRT observations
DATE:    21/04/23 15:32:05 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai
(INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B.
Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester) and P.A. Evans (U. Leicester) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Swift/BAT-detected burst GRB 210421B (James DeLaunay et al. GCN Circ.
29877), collecting 2.0 ks of Photon Counting (PC) mode data between
T0+45.1 ks and T0+85.2 ks. 

No X-ray sources have been detected. The 3-sigma upper limit in the
field ranges from ~0.004 to ~0.008 ct s^-1, corresponding to a 0.3-10
keV observed flux of 1.6e-13 to 3.4e-13 erg cm^-2 s^-1 (assuming a
typical GRB spectrum).

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021429.

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