GCN Circular 14053
M.C. Stroh (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (ASDC), V. Mangano (INAF-IASFPA), J.A. Kennea (PSU) and A. Maselli report on behalf of the Swift-XRT team: We have analysed 18 ks of XRT data for GRB 121209A (Maselli et al. GCN Circ. 14045), from 95 s to 48.0 ks after the BAT trigger. The data comprise 28 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 14051). The late-time light curve (from T0+5.2 ks) can be modelled with a power-law decay with a decay index of alpha=1.20 (+/-0.06). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.31 (+/-0.14). The best-fitting absorption column is 5.3 (+/-0.6) x 10^21 cm^-2, in excess of the Galactic value of 3.8 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (9.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.3 (+/-0.6) x 10^21 cm^-2 Galactic foreground: 3.8 x 10^20 cm^-2 Excess significance: 13.4 sigma Photon index: 2.31 (+/-0.14) If the light curve continues to decay with a power-law decay index of 1.20, the count rate at T+24 hours will be 0.014 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.8 x 10^-13 (1.3 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/00540964. This circular is an official product of the Swift-XRT team.