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GCN Circular 29427

Subject
GRB 210207B: Swift-XRT refined Analysis
Date
2021-02-08T13:40:11Z (3 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
K.L. Page (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &
INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (PSU), D.N.
Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester), P.A.
Evans (U. Leicester) and A.Y. Lien report on behalf of the Swift-XRT
team:

We have analysed 6.8 ks of XRT data for GRB 210207B (Lien et al. GCN
Circ. 29420), from 80 s to 45.6 ks after the  BAT trigger. The data
comprise 329 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Beardmore et al. (GCN Circ. 29422).

The late-time light curve (from T0+3.9 ks) can be modelled with a
power-law decay with a decay index of alpha=1.37 (+0.07, -0.06).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.99 (+/-0.04). The
best-fitting absorption column is  1.38 (+/-0.13) x 10^21 cm^-2, in
excess of the Galactic value of 3.5 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.78 (+0.11, -0.10)
and a best-fitting absorption column of 7.2 (+2.9, -2.6) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.7 x 10^-11 (4.2 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.2 (+2.9, -2.6) x 10^20 cm^-2
Galactic foreground: 3.5 x 10^20 cm^-2
Excess significance: 2.3 sigma
Photon index:	     1.78 (+0.11, -0.10)

If the light curve continues to decay with a power-law decay index of
1.37, the count rate at T+24 hours will be 0.021 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.7 x
10^-13 (8.7 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01031297.

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