TITLE: GCN CIRCULAR NUMBER: 20997 SUBJECT: GRB 170405A: Swift-XRT refined Analysis DATE: 17/04/06 17:03:32 GMT FROM: Phil Evans at U of Leicester K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Cholden-Brown (PSU), S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Mingo (U. Leicester), A.P. Beardmore (U. Leicester) and report on behalf of the Swift-XRT team: report on behalf of the Swift-XRT team: We have analysed 6.5 ks of XRT data for GRB 170405A, from 111 s to 57.3 ks after the BAT trigger. The data comprise 489 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+4.5 ks) can be modelled with a power-law decay with a decay index of alpha=1.66 (+0.14, -0.12). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.592 (+0.027, -0.019). The best-fitting absorption column is consistent with the Galactic value of 8.7 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.84 (+0.09, -0.07) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 8.7 x 10^20 cm^-2 Intrinsic column: 8.7 (+68.1, -0.0) x 10^20 cm^-2 at z=3.51 Photon index: 1.84 (+0.09, -0.07) If the light curve continues to decay with a power-law decay index of 1.66, the count rate at T+24 hours will be 5.5 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.0 x 10^-13 (2.3 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00745797. This circular is an official product of the Swift-XRT team.