GCN Circular 20431

P.A. Evans (U. Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A.
Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU),
T.G.R. Roegiers (PSU), S.L. Gibson (U. Leicester), J.P. Osborne (U.
Leicester) and	report on behalf of the Swift-XRT team: report on
behalf of the Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 170111A, from 96 s to 42.0
ks after the  BAT trigger. The data comprise 17 s in Windowed Timing
(WT) mode (the first 4 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+5.1 ks) can be modelled with a
power-law decay with a decay index of alpha=0.72 (+/-0.18).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.68 (+0.17, -0.16). The
best-fitting absorption column is  3.6 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 3.1 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 4.6 x 10^-11 (6.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.6 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 3.1 x 10^20 cm^-2
Excess significance: 6.6 sigma
Photon index:	     1.68 (+0.17, -0.16)

If the light curve continues to decay with a power-law decay index of
0.72, the count rate at T+24 hours will be 0.020 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.5 x
10^-13 (1.2 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/00731887.

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