TITLE: GCN CIRCULAR NUMBER: 29427 SUBJECT: GRB 210207B: Swift-XRT refined Analysis DATE: 21/02/08 13:40:11 GMT FROM: Phil Evans at U of Leicester K.L. Page (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester) and A.Y. Lien report on behalf of the Swift-XRT team: We have analysed 6.8 ks of XRT data for GRB 210207B (Lien et al. GCN Circ. 29420), from 80 s to 45.6 ks after the BAT trigger. The data comprise 329 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. 29422). The late-time light curve (from T0+3.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.37 (+0.07, -0.06). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.99 (+/-0.04). The best-fitting absorption column is 1.38 (+/-0.13) x 10^21 cm^-2, in excess of the Galactic value of 3.5 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.78 (+0.11, -0.10) and a best-fitting absorption column of 7.2 (+2.9, -2.6) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.2 (+2.9, -2.6) x 10^20 cm^-2 Galactic foreground: 3.5 x 10^20 cm^-2 Excess significance: 2.3 sigma Photon index: 1.78 (+0.11, -0.10) If the light curve continues to decay with a power-law decay index of 1.37, the count rate at T+24 hours will be 0.021 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.7 x 10^-13 (8.7 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/01031297. This circular is an official product of the Swift-XRT team.