TITLE: GCN CIRCULAR NUMBER: 29449 SUBJECT: GRB 210209A: Swift-XRT refined Analysis DATE: 21/02/10 08:13:33 GMT FROM: Phil Evans at U of Leicester M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester) and S. Laha report on behalf of the Swift-XRT team: We have analysed 6.3 ks of XRT data for GRB 210209A (Laha et al. GCN Circ. 29442), from 122 s to 24.0 ks after the BAT trigger. The data comprise 139 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 29443). The late-time light curve (from T0+4.3 ks) can be modelled with a power-law decay with a decay index of alpha=0.88 (+/-0.09). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.81 (+0.07, -0.04). The best-fitting absorption column is consistent with the Galactic value of 3.7 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.91 (+0.07, -0.05) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.67 (+0.14, -0.00) x 10^21 cm^-2 Galactic foreground: 3.7 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.91 (+0.07, -0.05) If the light curve continues to decay with a power-law decay index of 0.88, the count rate at T+24 hours will be 0.046 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x 10^-12 (2.6 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01031636. This circular is an official product of the Swift-XRT team.