TITLE: GCN CIRCULAR NUMBER: 20963 SUBJECT: GRB 170330A: Swift-XRT refined Analysis DATE: 17/03/31 18:51:53 GMT FROM: Phil Evans at U of Leicester J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D.N. Burrows (PSU), A. Cholden-Brown (PSU), S. J. LaPorte (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 7.3 ks of XRT data for GRB 170330A, from 89 s to 53.1 ks after the BAT trigger. The data comprise 404 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=0.71 (+0.07, -0.06), followed by a break at T+439 s to an alpha of 1.061 (+0.029, -0.025). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.00 (+/-0.10). The best-fitting absorption column is 4.0 (+0.6, -0.5) x 10^21 cm^-2, in excess of the Galactic value of 3.0 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.88 (+0.12, -0.11) and a best-fitting absorption column of 4.0 (+/-0.6) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.2 x 10^-11 (6.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.0 (+/-0.6) x 10^21 cm^-2 Galactic foreground: 3.0 x 10^21 cm^-2 Excess significance: 2.6 sigma Photon index: 1.88 (+0.12, -0.11) If the light curve continues to decay with a power-law decay index of 1.061, the count rate at T+24 hours will be 0.021 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.7 x 10^-13 (1.3 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/00744773. This circular is an official product of the Swift-XRT team.