GCN Circular 20470
K.L. Page and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 3.9 ks of XRT data for GRB 170115A, from 82 s to 40.4 ks after the BAT trigger. The data comprise 224 s in Windowed Timing (WT) mode (the first 7 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.54 (+0.06, -0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.22 (+0.17, -0.16). The best-fitting absorption column is 1.3 (+0.5, -0.4) x 10^21 cm^-2, in excess of the Galactic value of 6.1 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 2.9 x 10^-11 (4.0 x 10^-11) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 1.3 (+0.5, -0.4) x 10^21 cm^-2 Galactic foreground: 6.1 x 10^20 cm^-2 Excess significance: 2.6 sigma Photon index: 2.22 (+0.17, -0.16) If the light curve continues to decay with a power-law decay index of 1.54, the count rate at T+24 hours will be 4.1 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x 10^-14 (1.7 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/00733103. This circular is an official product of the Swift-XRT team.