TITLE: GCN CIRCULAR NUMBER: 41280 SUBJECT: GRB 250807B: Swift-XRT refined Analysis DATE: 25/08/08 09:17:21 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), D.N. Burrows (PSU), M.A. Williams (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.3 ks of XRT data for GRB 250807B, from 133 s to 50.6 ks after the trigger. The data comprise 188 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+3.8 ks) can be modelled with a power-law decay with a decay index of alpha=1.16 (+0.14, -0.13). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.96 (+/-0.07). The best-fitting absorption column is 4.2 (+1.5, -1.4) x 10^20 cm^-2, in excess of the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.97 (+0.21, -0.19) and a best-fitting absorption column of 5.8 (+4.7, -4.0) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (3.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.8 (+4.7, -4.0) x 10^20 cm^-2 Galactic foreground: 1.9 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.97 (+0.21, -0.19) If the light curve continues to decay with a power-law decay index of 1.16, the count rate at T+24 hours will be 6.4 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.1 x 10^-13 (2.4 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/01340561. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41280. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...