TITLE:   GCN CIRCULAR
NUMBER:  29278
SUBJECT: GRB 201216C: Swift-XRT refined Analysis
DATE:    21/01/08 02:49:56 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), M.G. Bernardini
(INAF-OAB), E. Ambrosi	(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), A.
Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), D.N. Burrows (PSU) and
A.P. Beardmore report on behalf of the Swift-XRT team:

We have analysed 2.8 ks of XRT data for GRB 201216C (Beardmore et al.
GCN Circ. 29061), from 3.0 ks to 1896.5 ks after the  BAT trigger. The
data comprise 466 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN Circ. 29067).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.97 (+0.10, -0.09).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.35 (+0.17, -0.16). The
best-fitting absorption column is  7.7 (+1.2, -1.1) x 10^21 cm^-2, in
excess of the Galactic value of 5.0 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.03 (+0.16, -0.15)
and a best-fitting absorption column of 5.6 (+1.0, -0.9) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.2 x 10^-11 (8.0 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.6 (+1.0, -0.9) x 10^21 cm^-2
Galactic foreground: 5.0 x 10^20 cm^-2
Excess significance: 9.3 sigma
Photon index:	     2.03 (+0.16, -0.15)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01013243.

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