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GCN Circular 26285

Subject
GRB 191123A: Swift-XRT refined Analysis
Date
2019-11-23T20:52:37Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAB), P. D'Avanzo (INAF-OAB), B. Sbarufatti (PSU), D.N. Burrows
(PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and A. Tohuvavohu report on behalf of the Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 191123A (Tohuvavohu et al.
GCN Circ. 26279), from 76 s to 18.5 ks after the  BAT trigger. The data
comprise 540 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 26284).

The late-time light curve (from T0+5.6 ks) can be modelled with a
power-law decay with a decay index of alpha=1.00 (+/-0.15).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.52 (+/-0.05). The
best-fitting absorption column is  6.7 (+1.6, -1.5) x 10^20 cm^-2, in
excess of the Galactic value of 3.0 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.98 (+0.12, -0.11)
and a best-fitting absorption column of 4.8 (+2.6, -1.8) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.3 x 10^-11 (3.7 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.8 (+2.6, -1.8) x 10^20 cm^-2
Galactic foreground: 3.0 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.98 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
1.00, the count rate at T+24 hours will be 0.022 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.2 x
10^-13 (8.1 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00939079.

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