TITLE: GCN CIRCULAR NUMBER: 29807 SUBJECT: GRB 210411C: Swift-XRT refined Analysis DATE: 21/04/12 15:33:49 GMT FROM: Phil Evans at U of Leicester J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB) and T. Sbarrato report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 210411C (Sbarrato et al. GCN Circ. 29794), from 66 s to 42.0 ks after the BAT trigger. The data comprise 136 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 29800). The late-time light curve (from T0+5.4 ks) can be modelled with a power-law decay with a decay index of alpha=1.49 (+/-0.17). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.66 (+0.19, -0.18). The best-fitting absorption column is 1.2 (+0.4, -0.3) x 10^21 cm^-2, in excess of the Galactic value of 8.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.84 (+0.14, -0.11) and a best-fitting absorption column of 9.4 (+4.0, -1.3) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 9.4 (+4.0, -1.3) x 10^20 cm^-2 Galactic foreground: 8.1 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.84 (+0.14, -0.11) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01042398. This circular is an official product of the Swift-XRT team.