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GCN Circular 33584

Subject
GRB 230405B: Swift-XRT refined Analysis
Date
2023-04-07T02:01:14Z (a year ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB), M.G. Bernardini (INAF-OAB), A. Tohuvavohu (U. Toronto),
D.N. Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester) and
K.L. Page report on behalf of the Swift-XRT team:

We have analysed 6.5 ks of XRT data for GRB 230405B (Page et al. GCN
Circ. 33571), from 54 s to 75.0 ks after the  BAT trigger. The data
comprise 246 s in Windowed Timing (WT) mode (the first 10 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. 33572).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.88 (+/-0.04), followed by a break at T+937 s to an
alpha of 1.14 (+0.16, -0.05).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.10 (+0.12, -0.11). The
best-fitting absorption column is  4.0 (+0.6, -0.5) x 10^21 cm^-2, in
excess of the Galactic value of 1.6 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.95 (+0.17, -0.16)
and a best-fitting absorption column of 5.4 (+1.1, -1.0) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.2 x 10^-11 (6.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.4 (+1.1, -1.0) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^21 cm^-2
Excess significance: 6.2 sigma
Photon index:	     1.95 (+0.17, -0.16)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01163119.

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