TITLE: GCN CIRCULAR NUMBER: 13972 SUBJECT: GRB 121117A: Swift-XRT refined Analysis DATE: 12/11/18 08:37:46 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore (U. Leicester) and J. R. Cummings (NASA/UMBC) report on behalf of the Swift-XRT team: We have analysed 13 ks of XRT data for GRB 121117A (Cummings et al. GCN Circ. 13967), from 41 s to 62.7 ks after the BAT trigger. The data comprise 204 s in Windowed Timing (WT) mode (the first 5 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. Using 3463 s of PC mode data and 6 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 31.61064, +7.41954 which is equivalent to: RA (J2000): 02h 06m 26.55s Dec(J2000): +07d 25' 10.4" with an uncertainty of 1.7 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.27 (+/-0.04). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.55 (+0.22, -0.19). The best-fitting absorption column is 8.4 (+7.2, -3.2) x 10^20 cm^-2, consistent with the Galactic value of 5.2 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 4.2 x 10^-11 (4.7 x 10^-11) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 8.4 (+7.2, -3.2) x 10^20 cm^-2 Galactic foreground: 5.2 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.55 (+0.22, -0.19) If the light curve continues to decay with a power-law decay index of 1.27, the count rate at T+24 hours will be 9.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x 10^-14 (4.7 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00538696. This circular is an official product of the Swift-XRT team.