TITLE: GCN CIRCULAR NUMBER: 41935 SUBJECT: GRB 250920C: Swift-XRT refined Analysis DATE: 25/09/22 10:15:36 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.1 ks of XRT data for GRB 250920C, from 110 s to 131.0 ks after the trigger. The data comprise 64 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+7.1 ks) can be modelled with a power-law decay with a decay index of alpha=1.53 (+/-0.09). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.94 (+/-0.10). The best-fitting absorption column is 4.8 (+2.1, -2.0) x 10^20 cm^-2, in excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.89 (+0.16, -0.15) and a best-fitting absorption column of 6.7 (+4.0, -3.5) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.7 (+4.0, -3.5) x 10^20 cm^-2 Galactic foreground: 1.4 x 10^20 cm^-2 Excess significance: 2.5 sigma Photon index: 1.89 (+0.16, -0.15) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01351039. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41935. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...