TITLE: GCN CIRCULAR NUMBER: 9825 SUBJECT: GRB 090817: Confirmation of the X-ray afterglow DATE: 09/08/18 08:52:01 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), C. Guidorzi (U Ferrara) and W.H. Baumgartner (GSFC/UMBC) report on behalf of the Swift-XRT team: Swift conducted a second observation of GRB 090817 (Beckmann et al. GCN Circ. 9815), collecting 3.9 ks of Photon Counting (PC) mode XRT data in the interval T0+50 ks to T0+58 ks. The source reported by Evans et al. (GCN Circ. 9819) has faded to a level of ~0.015 ct s^-1. A power-law fit to the light curve yields a temporal decay index of alpha=0.9+/-0.2 Inspecting the USNO-B1 catalogue within 3.5' of the GRB we find 216 objects with R2<20.0. The probability of finding a USNO-B1 source within a 2" radius circle in this field is thus 2%. The strength of the potential association between the XRT and USNO-B1 sources noted in GCN Circ. 9819 is therefore fairly weak. We therefore suggest that the XRT source is the afterglow of GRB 090817. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020108. This circular is an official product of the Swift-XRT team.