TITLE: GCN CIRCULAR NUMBER: 20164 SUBJECT: GRB 161109A: Swift-XRT observations DATE: 16/11/10 08:00:39 GMT FROM: Antonino D'Ai at IASF-PA S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 161109A (Desiante et al. GCN Circ. 20155) in a series of observations tiled on the sky. The total exposure time is 4.1 ks, distributed over 5 tiles; the maximum exposure at a single sky location was 2.9 ks. The data were collected between T0+40.4 ks and T0+63.6 ks, and are entirely in Photon Counting (PC) mode. Three uncatalogued X-ray sources have been detected, however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below: Source 2: RA (J2000.0): 157.9051 = 10:31:37.24 Dec (J2000.0): +61.8845 = +61:53:04.4 Error: 3.7 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (6.1 [+3.2, -2.4])e-3 ct s^-1 Distance: 244 arcsec from Fermi/LAT position. Source 5: RA (J2000.0): 157.9726 = 10:31:53.43 Dec (J2000.0): +61.9393 = +61:56:21.6 Error: 6.4 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (6.6 [+2.6, -2.1])e-3 ct s^-1 Distance: 471 arcsec from Fermi/LAT position. Source 6: RA (J2000.0): 158.0653 = 10:32:15.66 Dec (J2000.0): +61.6754 = +61:40:31.5 Error: 6.9 arcsec (radius, 90% conf.) Count-rate: (6.8 [+3.1, -2.4])e-3 ct s^-1 Distance: 635 arcsec from Fermi/LAT position. Flux: (2.01 [+0.91, -0.70])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Three catalogued sources were also detected. The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at http://www.swift.ac.uk/xrt_products/TILED_GRB00060. This circular is an official product of the Swift-XRT team.