TITLE: GCN CIRCULAR NUMBER: 10177 SUBJECT: GRB 091117: Swift XRT refined analysis DATE: 09/11/19 15:58:16 GMT FROM: Valerio D'Elia at INAF-OAR V. D'Elia, G. Stratta, M. Perri (ASDC), P.A. Evans and M.R. Goad (U. Leicester), J. Cummings (GSFC/CRESST), S. Campana (INAF-OAB) report on behalf of the Swift-XRT team: We have analysed 3.85 ks of XRT data for GRB 091117 (Cummings et al. et al. GCN Circ. 10171), from 96765 s to 119.4 ks after the Suzaku trigger. The data are entirely in Photon Counting (PC) mode. Two sources are detected at the edge of the BAT error circle. Source #1: using 722 s of XRT Photon Counting mode data and 1 UVOT images, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 30.97240, -16.97490 deg which is equivalent to: RA (J2000): 02 03 53.38 Dec (J2000): -16 58 29.8 with an uncertainty of 3.6 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). The source is at a count rate level of (4.8+/-1.4)e-3 counts/s. The light curve does not allow us to assess if the source is fading. This source has been reported by Berger et al. (GCN Circ. 10173) to be coincident with the DSS galaxy APMUKS B020129.84-171252.3 at redshift z=0.096 (Chornock & Berger 2009, GCN Circ. 10176) We can't distinguish if this is nuclear emission from the AGN discussed by Berger et al. (GCN Circ. 10176) Source #2: the other source has a count rate level of (2.7+/-1.1)e-3 counts/s and is at RA, Dec= 30.988333, -16.948583 deg which is equivalent to RA (J2000): 02 03 57.2 Dec(J2000): -16 56 54.9 with an uncertainty of 7.7 arcsec (radius, 90% confidence). The light curve does not allow us to assess if the source is fading. We note that there is a known source (2MASX J02035665-1656585 at z=0.096220) located 8.8 arcsec from Source #2. Further observations are planned for this field. This circular is an official product of the Swift-XRT team.