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GCN Circular 34995

Subject
GRB 231111A: Swift-XRT refined Analysis
Date
2023-11-12T04:47:24Z (7 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB), A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp
(PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 7.3 ks of XRT data for GRB 231111A, from 93 s to 39.7
ks after the  BAT trigger. The data comprise 296 s in Windowed Timing
(WT) mode (the first 5 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+16.2 ks) can be modelled with a
power-law decay with a decay index of alpha=1.03 (+/-0.23).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.47 (+0.10, -0.06). The
best-fitting absorption column is  1.297 (+0.206, -0.027) x 10^21
cm^-2, consistent with the Galactic value of 1.3 x 10^21 cm^-2
(Willingale et al. 2013). The PC mode spectrum has a photon index of
1.98 (+0.19, -0.18) and a best-fitting absorption column of 1.6 (+0.6,
-0.3) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum  is 3.5 x 10^-11 (4.6
x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+0.6, -0.3) x 10^21 cm^-2
Galactic foreground: 1.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.98 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
1.03, the count rate at T+24 hours will be 0.029 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 10.0 x
10^-13 (1.3 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01195887.

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

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