TITLE: GCN CIRCULAR NUMBER: 15351 SUBJECT: GRB 131014A: XRT position information DATE: 13/10/18 13:30:03 GMT FROM: Phil Evans at U of Leicester P.A. Evans and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team The Swift-XRT localisation of GRB 131014A has unusually significant uncertainty, which is not included in the positions previously circulated (GCNs 15335, 15339), or on the website. The afterglow was detected towards the edge of two of the initial tiled pointings, and near the centre of a dedicated follow-up pointing. Positions derived from these individual pointings vary by up to 4" when the Swift star tracker attitude is used. If we instead create enhanced positions (using the UVOT to derive the astrometry) we find astrometric corrections of ~5-8", although we find significant variation between these corrections. This suggests that there is some degeneracy in the aspect solution. Given this variation we suggest that the XRT position should be assumed to have an uncertainty of 6", rather than the values previously announced or posted online. Thus the best available XRT position is RA, Dec=100.3033, -19.0971, which is equivalent to: RA: 06h 41m 12.80s Dec: -19° 05′ 49.6′′ with an uncertainty of approx 6". This is the enhanced position derived from the follow-up observation, which was centred on the afterglow. Some low-level scatter in the aspect solutions is seen in all enhanced positions, and is calibrated into our enhanced position errors. GRB 131014A shows an exceptionally large scatter in the aspect solutions which is not currently understood. Futhermore, as this is a late-time tiled follow up, where the source is faint and individual exposures are short, the normal mechanisms which remove outlying aspect solutions cannot be applied.