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GCN Circular 31281

Subject
GRB 211221A: Swift-XRT refined Analysis
Date
2021-12-22T22:38:35Z (3 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC &
INAF-OAR), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U.
Toronto), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester) and
K.L. Page report on behalf of the Swift-XRT team:

We have analysed 5.9 ks of XRT data for GRB 211221A (Page et al. GCN
Circ. 31273), from 44 s to 73.7 ks after the  BAT trigger. The data
comprise 52 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Evans et
al. (GCN Circ. 31275).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.02 (+0.05, -0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.59 (+0.31, -0.29). The
best-fitting absorption column is  1.1 (+0.4, -0.3) x 10^22 cm^-2, in
excess of the Galactic value of 1.4 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 6.2 x 10^-11 (9.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.1 (+0.4, -0.3) x 10^22 cm^-2
Galactic foreground: 1.4 x 10^21 cm^-2
Excess significance: 5.0 sigma
Photon index:	     1.59 (+0.31, -0.29)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01090472.

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