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GCN Circular 26027

GRB 191017B: Swift-XRT refined Analysis
2019-10-18T05:32:16Z (5 years ago)
Phil Evans at U of Leicester <>
A.P. Beardmore (U. Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA),
A. Melandri (INAF-OAB), D.N. Burrows (PSU), J. D. Gropp (PSU), A.
Tohuvavohu (U. Toronto), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester) and B. Sbarufatti report on behalf of the Swift-XRT team:

We have analysed 6.1 ks of XRT data for GRB 191017B (Sbarufatti et al.
GCN Circ. 26021), from 256 s to 29.2 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Goad et al. (GCN Circ. 26022).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.64 (+/-0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.54 (+0.20, -0.12). The
best-fitting absorption column is  consistent with the Galactic value
of 9.8 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 4.4 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.8 (+/-6.9) x 10^20 cm^-2
Galactic foreground: 9.8 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.54 (+0.20, -0.12)

If the light curve continues to decay with a power-law decay index of
0.64, the count rate at T+24 hours will be 0.018 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.8 x
10^-13 (8.6 x 10^-13) 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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