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GCN Circular 28508

GRB 200925B: Swift-XRT refined Analysis
2020-09-26T22:00:05Z (4 years ago)
Phil Evans at U of Leicester <>
B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P.
Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB) and S.B. Cenko report on behalf of the Swift-XRT team:

We have analysed 5.1 ks of XRT data for GRB 200925B (Cenko et al. GCN
Circ. 28499), from 87 s to 47.2 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Beardmore et al. (GCN Circ. 28500). The
late-time light curve (from T0+29.2 ks) is consistent with a constant
source of mean count rate 1.3e-01 ct/sec. A power-law fit gives an
index of 1.0 (+/-1.2).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.12 (+0.19, -0.18). The
best-fitting absorption column is  7.5 (+4.4, -2.9) x 10^20 cm^-2,
consistent with the Galactic value of 4.6 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 3.1 x 10^-11 (3.8 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.5 (+4.4, -2.9) x 10^20 cm^-2
Galactic foreground: 4.6 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.12 (+0.19, -0.18)

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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