TITLE: GCN CIRCULAR NUMBER: 22322 SUBJECT: GRB 180111A: Swift-XRT refined Analysis DATE: 18/01/12 01:25:41 GMT FROM: Phil Evans at U of Leicester S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA) and A.Y. Lien report on behalf of the Swift-XRT team: We have analysed 6.1 ks of XRT data for GRB 180111A (Lien et al. GCN Circ. 22318), from 94 s to 23.6 ks after the BAT trigger. The data comprise 117 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 22319). The late-time light curve (from T0+4.0 ks) can be modelled with a power-law decay with a decay index of alpha=1.46 (+0.38, -0.29). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.48 (+/-0.09). The best-fitting absorption column is 4.0 (+3.0, -2.6) x 10^20 cm^-2, in excess of the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.66 (+0.21, -0.12) and a best-fitting absorption column of 1.17 (+4.88, -0.09) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.8 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.17 (+4.88, -0.09) x 10^20 cm^-2 Galactic foreground: 1.1 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.66 (+0.21, -0.12) If the light curve continues to decay with a power-law decay index of 1.46, the count rate at T+24 hours will be 9.2 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.5 x 10^-14 (3.6 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/00804692. This circular is an official product of the Swift-XRT team.