TITLE: GCN CIRCULAR NUMBER: 14093 SUBJECT: GRB 121217A: Swift-XRT refined Analysis DATE: 12/12/17 21:32:04 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), O.M. Littlejohns (U. Leicester), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), G. Stratta (ASDC), M.C. Stroh (PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester) and M.H. Siegel report on behalf of the Swift-XRT team: We have analysed 7.1 ks of XRT data for GRB 121217A (Siegel et al. GCN Circ. 14089), from 70 s to 30.3 ks after the BAT trigger. The data comprise 655 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 14090). The late-time light curve (from T0+5.5 ks) can be modelled with a power-law decay with a decay index of alpha=0.63 (+/-0.08). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.15 (+0.11, -0.08). The best-fitting absorption column is consistent with the Galactic value of 3.7 x 10^21 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 1.92 (+0.11, -0.10) and a best-fitting absorption column of 4.02 (+0.51, -0.30) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.6 x 10^-11 (7.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.02 (+0.51, -0.30) x 10^21 cm^-2 Galactic foreground: 3.7 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.92 (+0.11, -0.10) If the light curve continues to decay with a power-law decay index of 0.52, the count rate at T+24 hours will be 0.091 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x 10^-12 (6.7 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/00542441. This circular is an official product of the Swift-XRT team.