TITLE: GCN CIRCULAR NUMBER: 20431 SUBJECT: GRB 170111A: Swift-XRT refined Analysis DATE: 17/01/11 17:52:10 GMT FROM: Phil Evans at U of Leicester 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.