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GCN Circular 25998

Subject
GRB 191011A: Swift-XRT refined Analysis
Date
2019-10-11T13:13:26Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore
(U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (ASDC), V. D'Elia
(ASDC), J.A. Kennea (PSU), B. Sbarufatti (PSU), D.N. Burrows (PSU) and
S.L Laha report on behalf of the Swift-XRT team:

We have analysed 7.1 ks of XRT data for GRB 191011A (L Laha et al. GCN
Circ. 25988), from 84 s to 23.3 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Evans et al. (GCN Circ. 25995).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.15 (+0.15, -0.20), followed by a break at T+855 s to
an alpha of 1.34 (+/-0.12).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.83 (+/-0.15). The
best-fitting absorption column is  5.3 (+3.5, -3.1) x 10^21 cm^-2, at a
redshift of 1.722, in addition to the Galactic value of 1.5 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 (4.1 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.5 x 10^20 cm^-2
Intrinsic column:    5.3 (+3.5, -3.1) x 10^21 cm^-2 at z=1.722
Photon index:	     1.83 (+/-0.15)

If the light curve continues to decay with a power-law decay index of
1.34, the count rate at T+24 hours will be 1.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.7 x
10^-14 (4.2 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00928924.

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