GCN Circular 31861
Subject
GRB 220408A: Swift-XRT refined Analysis
Date
2022-04-09T08:44:36Z (3 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &
INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (PSU), D.N.
Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester), K.L.
Page (U. Leicester) and R. Caputo report on behalf of the Swift-XRT
team:
We have analysed 7.5 ks of XRT data for GRB 220408A (Caputo et al. GCN
Circ. 31848), from 93 s to 63.6 ks after the BAT trigger. The data
comprise 10 s in Windowed Timing (WT) mode (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.
31852).
The light curve can be modelled with an initial power-law decay with an
index of alpha=0.46 (+0.16, -0.17), followed by a break at T+2306 s to
an alpha of 1.37 (+0.16, -0.15).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.94 (+0.23, -0.22). The
best-fitting absorption column is 1.8 (+0.8, -0.7) x 10^21 cm^-2, in
excess of the Galactic value of 2.0 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 3.6 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.8 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 2.0 x 10^20 cm^-2
Excess significance: 3.8 sigma
Photon index: 1.94 (+0.23, -0.22)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01101675.
This circular is an official product of the Swift-XRT team.