TITLE: GCN CIRCULAR NUMBER: 41170 SUBJECT: GRB 250725A: Swift-XRT refined Analysis DATE: 25/07/25 19:07:22 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.4 ks of XRT data for GRB 250725A, from 828 s to 53.2 ks after the trigger. The data comprise 64 s in Windowed Timing (WT) mode 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=1.14 (+/-0.06), followed by a break at T+13.4 ks to an alpha of 2.2 (+0.4, -0.3). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.72 (+0.09, -0.08). The best-fitting absorption column is 2.7 (+2.3, -2.1) x 10^22 cm^-2, at a redshift of 5.26, in addition to the Galactic value of 9.2 x 10^20 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 (4.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 9.2 x 10^20 cm^-2 Intrinsic column: 2.7 (+2.3, -2.1) x 10^22 cm^-2 at z=5.26 Photon index: 1.72 (+0.09, -0.08) If the light curve continues to decay with a power-law decay index of 2.2, the count rate at T+24 hours will be 4.0 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x 10^-13 (1.9 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/01336720. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41170. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...