TITLE: GCN CIRCULAR NUMBER: 39221 SUBJECT: GRB 250207A: Swift-XRT refined Analysis DATE: 25/02/08 01:34:17 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.0 ks of XRT data for GRB 250207A, from 100 s to 73.6 ks after the BAT trigger. The data comprise 370 s in Windowed Timing (WT) mode (the first 4 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+4.2 ks) can be modelled with a power-law decay with a decay index of alpha=1.22 (+0.13, -0.10). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.14 (+/-0.06). The best-fitting absorption column is 6.7 (+/-1.2) x 10^20 cm^-2, in excess of the Galactic value of 2.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.02 (+0.16, -0.15) and a best-fitting absorption column of 5.5 (+3.5, -3.1) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (3.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.5 (+3.5, -3.1) x 10^20 cm^-2 Galactic foreground: 2.4 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.02 (+0.16, -0.15) If the light curve continues to decay with a power-law decay index of 1.22, the count rate at T+24 hours will be 0.010 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.4 x 10^-13 (3.9 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/01287821. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...