TITLE: GCN CIRCULAR NUMBER: 28508 SUBJECT: GRB 200925B: Swift-XRT refined Analysis DATE: 20/09/26 22:00:05 GMT FROM: Phil Evans at U of Leicester B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB) and S.B. Cenko report on behalf of the Swift-XRT team: We have analysed 5.1 ks of XRT data for GRB 200925B (Cenko et al. GCN Circ. 28499), from 87 s to 47.2 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 28500). The late-time light curve (from T0+29.2 ks) is consistent with a constant source of mean count rate 1.3e-01 ct/sec. A power-law fit gives an index of 1.0 (+/-1.2). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.12 (+0.19, -0.18). The best-fitting absorption column is 7.5 (+4.4, -2.9) x 10^20 cm^-2, consistent with the Galactic value of 4.6 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 3.1 x 10^-11 (3.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.5 (+4.4, -2.9) x 10^20 cm^-2 Galactic foreground: 4.6 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.12 (+0.19, -0.18) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00997453. This circular is an official product of the Swift-XRT team.