GCN Circular 10719
J. Mao (INAF-OAB) reports on behalf of the Swift-XRT team: We have analysed 8.7 ks of Swift XRT data for GRB 100504A (Mao et al. GCN Circ. 10712). The data comprise 120 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The light curve shows evidence of flaring in WT mode, peaking at about 83 s, after that, the light curve can be modelled with a broken power-law in PC mode, with an initial decay index of alpha1=3.04(+/-0.57) and breaking to a decay of index alpha2=0.57(+/-0.06), the break time is about 450 s. A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.95 (+/-0.09). The best-fitting absorption column is 9.07 (+/-0.71) x 10^21 cm^-2, in excess of the Galactic value of 3.77 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.96 x 10^-11 (9.31 x 10^-11) erg cm^-2 count^-1. The spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.40 (+/-0.37) and the absorption column density is consistent with the Galactic one in the GRB direction. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.56 x 10^-11 (6.72 x 10^-11) erg cm^-2 count^-1. If the light curve continues to decay with a power-law decay index of 0.57, the count rate at T+24 hours will be 6.9 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 x 10^-13 (4.6 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/00421124. This circular is an official product of the Swift-XRT team.