TITLE: GCN CIRCULAR NUMBER: 41719 SUBJECT: GRB 250904A: Swift-XRT refined Analysis DATE: 25/09/05 09:20:44 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.0 ks of XRT data for GRB 250904A, from 66 s to 45.6 ks after the trigger. The data comprise 9 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=0.85 (+0.05, -0.04). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.05 (+0.27, -0.25). The best-fitting absorption column is 4.4 (+1.4, -1.0) x 10^21 cm^-2, consistent with the Galactic value of 3.3 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (6.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.4 (+1.4, -1.0) x 10^21 cm^-2 Galactic foreground: 3.3 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.05 (+0.27, -0.25) If the light curve continues to decay with a power-law decay index of 0.85, the count rate at T+24 hours will be 7.0 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x 10^-13 (4.5 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/01347179. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41719. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...