TITLE: GCN CIRCULAR NUMBER: 20558 SUBJECT: GRB 170127A: Swift-XRT refined Analysis DATE: 17/01/28 11:12:10 GMT FROM: Phil Evans at U of Leicester J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), B. Mingo (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 170127A, from 86 s to 58.8 ks after the BAT trigger. The data comprise 168 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 an initial power-law decay with an index of alpha=1.28 (+/-0.15), followed by a break at T+329 s to an alpha of 8.0 (+0.0, -1.1). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.49 (+/-0.10). The best-fitting absorption column is 1.3 (+/-0.4) x 10^21 cm^-2, in excess of the Galactic value of 8.5 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 4.5 x 10^-11 (5.0 x 10^-11) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 1.3 (+/-0.4) x 10^21 cm^-2 Galactic foreground: 8.5 x 10^20 cm^-2 Excess significance: 2.0 sigma Photon index: 1.49 (+/-0.10) If the light curve continues to decay with a power-law decay index of 5.19, the count rate at T+24 hours will be 2.0 x 10^-13 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.9 x 10^-24 (10.0 x 10^-24) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00735326. This circular is an official product of the Swift-XRT team.