TITLE: GCN CIRCULAR NUMBER: 35127 SUBJECT: GRB 231118A: Swift-XRT refined Analysis DATE: 23/11/19 19:16:02 GMT FROM: Phil Evans at U of Leicester A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.0 ks of XRT data for GRB 231118A, from 86 s to 81.5 ks after the BAT trigger. The data comprise 117 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with an initial power-law decay with an index of alpha=0.84 (+/-0.05), followed by a break at T+8184 s to an alpha of 1.6 (+0.4, -0.3). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.36 (+0.14, -0.13). The best-fitting absorption column is 8.6 (+3.4, -2.8) x 10^21 cm^-2, at a redshift of 0.8304, in addition to the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.51 (+0.13, -0.12) and a best-fitting absorption column of 8.9 (+2.5, -2.2) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.8 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 1.9 x 10^20 cm^-2 Intrinsic column: 8.9 (+2.5, -2.2) x 10^21 cm^-2 at z=0.8304 Photon index: 1.51 (+0.13, -0.12) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01197311. This circular is an official product of the Swift-XRT team.