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GCN Circular 34944

GRB 231104A: Swift-XRT refined Analysis
2023-11-04T16:55:30Z (8 months ago)
Phil Evans at U of Leicester <>
J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V.
D'Elia (SSDC & INAF-OAR), A. Tohuvavohu (U. Toronto), D.N. Burrows
(PSU) and P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 6.6 ks of XRT data for GRB 231104A, from 72 s to 34.5
ks after the  BAT trigger. The data comprise 62 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 late-time light curve (from T0+10.9 ks) can be modelled with a
power-law decay with a decay index of alpha=1.08 (+/-0.22).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.93 (+0.28, -0.27). The
best-fitting absorption column is  7.9 (+1.1, -1.0) x 10^22 cm^-2, in
excess of the Galactic value of 1.3 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 9.9 x 10^-11 (3.0 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.9 (+1.1, -1.0) x 10^22 cm^-2
Galactic foreground: 1.3 x 10^21 cm^-2
Excess significance: 12.5 sigma
Photon index:	     1.93 (+0.28, -0.27)

If the light curve continues to decay with a power-law decay index of
1.08, the count rate at T+24 hours will be 0.017 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-12 (5.0 x 10^-12) erg cm^-2 s^-1.

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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