TITLE: GCN CIRCULAR NUMBER: 42017 SUBJECT: GRB 250925A: Swift-XRT refined Analysis DATE: 25/09/27 18:53:06 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> A. Melandri (INAF-OAR), S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.8 ks of XRT data for GRB 250925A, from 3.7 ks to 172.4 ks after the trigger. The data are entirely in Photon Counting (PC) mode. Using 4854 s of PC mode data and 10 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 341.21377, +46.55568 which is equivalent to: RA (J2000): 22h 44m 51.31s Dec(J2000): +46d 33' 20.5" with an uncertainty of 2.0 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=0.60 (+/-0.11). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.04 (+0.18, -0.17). The best-fitting absorption column is 3.1 (+0.7, -0.5) x 10^21 cm^-2, consistent with the Galactic value of 2.6 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 3.7 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.1 (+0.7, -0.5) x 10^21 cm^-2 Galactic foreground: 2.6 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.04 (+0.18, -0.17) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01352124. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42017. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...