TITLE: GCN CIRCULAR NUMBER: 16986 SUBJECT: GRB 141028A: Swift-XRT observations DATE: 14/10/29 16:39:33 GMT FROM: Claudio Pagani at U of Leicester C. Pagani, K. L. Page and P. A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 3.0 ks of XRT data for the Fermi/LAT-detected burst: GRB 141028A, from 31.0 ks to 71.7 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the Fermi/LAT error circle. Using 348 s of PC mode data and 1 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 = 322.60168, -0.23145 which is equivalent to: RA (J2000): 21h 30m 24.40s Dec(J2000): -00d 13' 53.2" with an uncertainty of 4.0 arcsec (radius, 90% confidence). This position is 367 arcsec from the Fermi/LAT position (Bissaldi et al. GCN 16969) and consistent with the positions of the optical counterpart detected by MASTER (Gorbovskoy et al. GCN 16972), GROND (Graham et al. GCN 16977) and UVOT (Siegel et al. GCN 16979). The light curve can be modelled with a power-law decay with a decay index of alpha=2.0 (+/-1.0). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.5 (+/-0.5). The best-fitting absorption column is 1.8 (+2.2, -1.3) x 10^21 cm^-2, in excess of the Galactic value of 4.1 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.0 x 10^-11 (5.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.8 (+2.2, -1.3) x 10^21 cm^-2 Galactic foreground: 4.1 x 10^20 cm^-2 Excess significance: 1.8 sigma Photon index: 2.5 (+/-0.5) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020420. This circular is an official product of the Swift-XRT team.