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GCN Circular 35127

GRB 231118A: Swift-XRT refined Analysis
2023-11-19T19:16:02Z (8 months ago)
Phil Evans at U of Leicester <>
A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB),
S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), K.L.
Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 5.0 ks of XRT data for GRB 231118A, from 86 s to 81.5
ks after the  BAT trigger. The data comprise 117 s in Windowed Timing
(WT) mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.84 (+/-0.05), followed by a break at T+8184 s to an
alpha of 1.6 (+0.4, -0.3).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.36 (+0.14, -0.13). The
best-fitting absorption column is  8.6 (+3.4, -2.8) x 10^21 cm^-2, at a
redshift of 0.8304, in addition to the Galactic value of 1.9 x 10^20
cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index
of 1.51 (+0.13, -0.12) and a best-fitting absorption column of 8.9
(+2.5, -2.2) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10
keV flux conversion factor deduced from this spectrum  is 4.8 x 10^-11
(5.7 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.9 x 10^20 cm^-2
Intrinsic column:    8.9 (+2.5, -2.2) x 10^21 cm^-2 at z=0.8304
Photon index:	     1.51 (+0.13, -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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