TITLE: GCN CIRCULAR NUMBER: 21086 SUBJECT: GRB 170510A: Swift-XRT observations DATE: 17/05/10 22:22:51 GMT FROM: Antonino D'Ai at IASF-PA A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A. Cholden-Brown (PSU), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) 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 170510A (Bissaldi et al. GCN Circ. 21080) in a series of observations tiled on the sky. The total exposure time is 4.7 ks, distributed over 7 tiles; the maximum exposure at a single sky location was 1.4 ks. The data were collected between T0+24.3 ks and T0+36.2 ks, and are entirely in Photon Counting (PC) mode. One uncatalogued X-ray source has been detected, it is below the RASS limit and shows no definitive signs of fading. Therefore, at the present time we cannot confirm this as the afterglow. Details of this source are given below: Source 1: RA (J2000.0): 160.15394 = 10:40:36.95 Dec (J2000.0): -39.21244 = -39:12:44.8 Error: 2.3 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: 0.0630 [+0.0091, -0.0090] ct s^-1 Distance: 794 arcsec from Fermi/LAT position. Flux: (1.76 [+0.26, -0.25])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV) Two 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_GRB00067. This circular is an official product of the Swift-XRT team.