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GCN Circular 29280

Subject
Correction to GCN 29278: GRB 201216C XRT refined analysis
Date
2021-01-08T11:59:30Z (3 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

The XRT refined analysis of GRB 201216C contained in GCN Circ. 29278
was incorrect, some of the data had been excluded from the analysis.
The corrected analysis is below.

We apologise for the confusion.


We have analysed 5.2 ks of XRT data for GRB 201216C (Beardmore et al.
GCN Circ. 29061), from 3.0 ks to 1938.0 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 an initial power-law decay with an
index of alpha=2.09 (+0.16, -0.10), followed by a break at T+9078 s to
an alpha of 1.07 (+0.15, -0.10).

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.
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