TITLE: GCN CIRCULAR NUMBER: 18191 SUBJECT: GRB 150821A: Enhanced Swift-XRT position DATE: 15/08/21 16:45:25 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 910 s of XRT Photon Counting mode data and 2 UVOT images for GRB 150821A, 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 = 341.91332, -57.89384 which is equivalent to: RA (J2000): 22h 47m 39.20s Dec (J2000): -57d 53' 37.8" with an uncertainty of 1.8 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). This circular was automatically generated, and is an official product of the Swift-XRT team.