TITLE: GCN CIRCULAR NUMBER: 19348 SUBJECT: GRB 160425A: Swift-XRT refined Analysis DATE: 16/04/26 07:23:07 GMT FROM: Phil Evans at U of Leicester A. Melandri (INAF-OAB), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), K.L. Page (U. Leicester), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and H.A. Krimm report on behalf of the Swift-XRT team: We have analysed 7.0 ks of XRT data for GRB 160425A (Krimm et al. GCN Circ. 19343), from 207 s to 18.4 ks after the BAT trigger. The data comprise 439 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 19347). The late-time light curve (from T0+6.1 ks) can be modelled with a power-law decay with a decay index of alpha=0.78 (+/-0.23). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.18 (+/-0.04). The best-fitting absorption column is 5.26 (+0.23, -0.22) x 10^21 cm^-2, in excess of the Galactic value of 7.7 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.76 (+0.19, -0.18) and a best-fitting absorption column of 5.7 (+/-0.8) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 2.9 x 10^-11 (9.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.7 (+/-0.8) x 10^21 cm^-2 Galactic foreground: 7.7 x 10^20 cm^-2 Excess significance: 10.6 sigma Photon index: 2.76 (+0.19, -0.18) If the light curve continues to decay with a power-law decay index of 0.78, the count rate at T+24 hours will be 0.019 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.5 x 10^-13 (1.7 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00684098. This circular is an official product of the Swift-XRT team.