TITLE: GCN CIRCULAR NUMBER: 28754 SUBJECT: GRB 201021C: Swift-XRT refined Analysis DATE: 20/10/22 20:40:03 GMT FROM: Phil Evans at U of Leicester D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , J. D. Gropp (PSU), J.A. Kennea (PSU) and A.Y. Lien report on behalf of the Swift-XRT team: We have analysed 4.3 ks of XRT data for GRB 201021C (Lien et al. GCN Circ. 28730), from 105 s to 58.8 ks after the BAT trigger. The data comprise 62 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 28736). The light curve can be modelled with a power-law decay with a decay index of alpha=1.22 (+0.07, -0.06). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.62 (+0.19, -0.16). The best-fitting absorption column is 5 (+21, -5) x 10^20 cm^-2, at a redshift of 1.07, in addition to the Galactic value of 2.0 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 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 2.0 x 10^20 cm^-2 Intrinsic column: 5 (+21, -5) x 10^20 cm^-2 at z=1.07 Photon index: 1.62 (+0.19, -0.16) 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 2.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-13 (1.1 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/01001130. This circular is an official product of the Swift-XRT team.