TITLE: GCN CIRCULAR NUMBER: 35757 SUBJECT: GRB 240218A: Swift-XRT refined Analysis DATE: 24/02/19 23:02:31 GMT FROM: Phil Evans at U of Leicester <pae9@star.le.ac.uk> K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), J. D. Gropp (PSU), S. Dichiara (PSU), J.A. Kennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.7 ks of XRT data for GRB 240218A, from 137 s to 149.4 ks after the BAT trigger. The data comprise 118 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) 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=2.12 (+0.11, -0.05), followed by a break at T+1538 s to an alpha of 0.70 (+0.06, -0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.39 (+/-0.04). The best-fitting absorption column is 1.39 (+0.29, -0.27) x 10^23 cm^-2, at a redshift of 6.782, in addition to the Galactic value of 4.2 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 4.8 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Galactic foreground: 4.2 x 10^20 cm^-2 Intrinsic column: 1.39 (+0.29, -0.27) x 10^23 cm^-2 at z=6.782 Photon index: 1.39 (+/-0.04) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01215912. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/35757. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...