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GCN Circular 30617

GRB 210807A: Swift-XRT refined Analysis
2021-08-08T12:24:18Z (3 years ago)
Phil Evans at U of Leicester <>
A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne
(U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi	(INAF-IASFPA) ,
M. Capalbi (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A.
Kennea (PSU) and A.Y. Lien report on behalf of the Swift-XRT team:

We have analysed 3.1 ks of XRT data for GRB 210807A (Lien et al. GCN
Circ. 30600), from 208 s to 86.2 ks after the  BAT trigger. The data
comprise 488 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 30603).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=0.71 (+/-0.09). At T+384 s  the decay
steepens to an alpha of 2.8 (+0.7, -0.6). The light curve breaks again
at T+497 s to a decay with alpha=1.02 (+/-0.03),  before a final break
at T+32.3 ks s after which the decay index is 2.1 (+1.0, -0.7).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.82 (+/-0.03). The
best-fitting absorption column is  5.52 (+0.24, -0.23) x 10^21 cm^-2,
in excess of the Galactic value of 3.4 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.71 (+0.15, -0.12)
and a best-fitting absorption column consistent with the Galactic
value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.6 x 10^-11 (5.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.4 (+0.6, -0.0) x 10^21 cm^-2
Galactic foreground: 3.4 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.71 (+0.15, -0.12)

The results of the XRT-team automatic analysis are available at

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