TITLE: GCN CIRCULAR NUMBER: 9046 SUBJECT: GRB 090328: Updated position/optical afterglow candidate DATE: 09/03/29 05:46:10 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT J. Kennea (PSU), P. Evans and M. Goad (U Leicester) report on behalf of the Swift/XRT Team: Further analysis of the candidate afterglow of GRB 090328 has been performed utilizing downlinked Swift XRT and UVOT data. Using 1329 s of XRT Photon Counting mode data and 2 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 = 90.66494, -41.88265 which is equivalent to: RA (J2000): 06 02 39.58 Dec (J2000): -41 52 57.5 with an uncertainty of 2.0 arcsec (radius, 90% confidence). Position enhancement is described by Goad et al. (2007, A&A, 476, 1401 http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an extension of this method. Swift/UVOT detects a point source at a location consistant with the XRT error circle, detected in the U and White filters. A catalogue search does not reveal any known source at the location of this source. We tentatively suggest that this UVOT source may be the optical afterglow of GRB 090328, although this cannot be confirmed until either the optical or X-ray afterglow candidates are seen to fade.