GRB 241213A: Swift-XRT refined Analysis

We have analysed 4.5 ks of XRT data for GRB 241213A, from 106 s to 33.0 ks after the BAT trigger. The data comprise 275 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The light curve can be modelled with an initial power-law decay with an index of alpha=0.59 (+0.07, -0.08), followed by a break at T+680 s to an alpha of 1.20 (+0.16, -0.06). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.89 (+/-0.10). The best-fitting absorption column is 3.3 (+0.5, -0.4) x 10^21 cm^-2, in excess of the Galactic value of 6.7 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.85 (+/-0.14) and a best-fitting absorption column of 3.9 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.3 x 10^-11 (6.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.9 (+0.8, -0.7) x 10^21 cm^-2 Galactic foreground: 6.7 x 10^20 cm^-2 Excess significance: 7.4 sigma Photon index: 1.85 (+/-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 5.9 x 10^-13 (8.5 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/01274039. This circular is an official product of the Swift-XRT team.