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GCN Circular 30776

Subject
GRB 210905A: Swift-XRT refined Analysis
Date
2021-09-06T01:28:59Z (3 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi 
(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR),
B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), P.A. Evans
(U. Leicester) and E. Sonbas report on behalf of the Swift-XRT team:

We have analysed 5.7 ks of XRT data for GRB 210905A (Sonbas et al. GCN
Circ. 30765), from 82 s to 84.8 ks after the  BAT trigger. The data
comprise 209 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 Beardmore
et al. (GCN Circ. 30768).

The late-time light curve (from T0+3.8 ks) can be modelled with a
power-law decay with a decay index of alpha=1.19 (+0.26, -0.27).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.44 (+0.05, -0.04). The
best-fitting absorption column is  3.8 (+1.8, -1.7) x 10^22 cm^-2, at a
redshift of 6.318, in addition to the Galactic value of 3.4 x 10^20
cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index
of 1.90 (+/-0.13) and a best-fitting absorption column of 2.9 (+3.7,
-2.9) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum  is 3.4 x 10^-11 (3.9
x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 3.4 x 10^20 cm^-2
Intrinsic column:    2.9 (+3.7, -2.9) x 10^22 cm^-2 at z=6.318
Photon index:	     1.90 (+/-0.13)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01071993.

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