TITLE: GCN CIRCULAR NUMBER: 42347 SUBJECT: GRB 251017A: Swift-XRT refined Analysis DATE: 25/10/18 08:54:16 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Capalbi (INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.3 ks of XRT data for GRB 251017A, from 96 s to 39.9 ks after the trigger. The data comprise 75 s in Windowed Timing (WT) mode (the first 11 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+4.7 ks) can be modelled with a power-law decay with a decay index of alpha=1.1 (+0.4, -0.3). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.67 (+/-0.15). The best-fitting absorption column is 1.4 (+/-0.5) x 10^21 cm^-2, consistent with the Galactic value of 8.9 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.09 (+0.22, -0.21) and a best-fitting absorption column of 1.9 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.9 (+0.8, -0.7) x 10^21 cm^-2 Galactic foreground: 8.9 x 10^20 cm^-2 Excess significance: 2.5 sigma Photon index: 2.09 (+0.22, -0.21) If the light curve continues to decay with a power-law decay index of 1.1, the count rate at T+24 hours will be 7.1 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.5 x 10^-13 (3.5 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01404904. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42347. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...