TITLE: GCN CIRCULAR NUMBER: 10342 SUBJECT: GRB 100117A: Swift-XRT refined analysis DATE: 10/01/18 14:44:00 GMT FROM: Boris Sbarufatti at INAF-IASF-Pa B. Sbarufatti, R. Margutti (INAF/OAB) and M. De Pasquale (UCL-MSSL) report on behalf of the Swift-XRT team: We have analysed 5.5 ks of XRT data for GRB 100117A (De Pasquale et al. GCN Circ. 10336), from 69 s to 18.9 ks after the BAT trigger. The data comprise 180 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The best position is the SPER UVOT enhanced position: RA,Dec = 11.2690, -1.5949 (degrees) which is equivalent to: RA (J2000) = 00 45 4.56 Dec (J2000) = -01 35 41.7 with an uncertainty of 2.4 arcsec (radius, 90% containment). This location is 50.8 arcseconds from the BAT ground position, inside the BAT error circle. After the initial flaring activity the light curve can be modeled with a power-law decay with a decay index of alpha=3.5 (+/-0.2). The afterglow is not detected after the first snapshot of data (ending 500 s after the trigger), with an upper limit of 5E-3 count/sec at ~12 ks after the trigger The spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.6 (+/-0.13). The best-fitting absorption column is 1.2 (+/-0.4) x 10^21 cm^-2, in excess of the Galactic value of 2.7 x 10^20 cm^-2 (Kalberla et al. 2005). The observed (unabsorbed) 0.3-10 keV flux is 4.14 (4.84) x 10^-10 erg cm^-2 s^-1. The spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.3 (-0.5+0.6). The best-fitting absorption column is 1.1 (+1.3-0.9) x 10^21 cm^-2, slightly in excess of the Galactic value of 2.7 x 10^20 cm^-2 (Kalberla et al. 2005). The observed (unabsorbed) 0.3-10 keV flux is 2.40 (3.54) x 10^-12 erg cm^-2 s^-1. The count-rate to flux conversion factor is 6.0E-11 erg cm^-2 count^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00382941 . This circular is an official product of the Swift-XRT team.