Astrometry plots showing the model-scaling fit results, with uninformative priors on jet parameters in the top panel, and priors informed by light-curve information in the bottom panel. Two different fits are shown in each: day 207 data omitted (black) and included (red). The closed circles are the flux centroids of a representative afterglow model resulting from the fit, for each epoch, and are anchored to the fitted location of the merger (rightmost open black circle, i.e., R.A._off and decl._off). Since ﹩\tfrac{{\theta }_{\,\rm{v}}}{{\theta }_{\rm{cp}\,}}﹩ is unconstrained in the black fit of the top panel, we set it to 15. For the “black” fits, we have included where the flux centroid at day 207 would be for that model for reference. The solid circles may not be perfectly aligned, given that the hydrodynamical model images used vary in pixel size between epochs. The open circles represent the astrometric nuisance parameters and indicate where the centroid would appear on the sky after including the systematic error inferred for the data on that epoch (δ_ra,i and δ_dec,i). The black X-shaped markers correspond to the image-plane positions of GW170817 from the VLBI data and the HST kilonova position (day 0, i.e., merger location). The 1σ uncertainty ellipse on each of these is determined using the values from Table 2, where the systematic error ellipse has been convolved with the statistical errors from the image-plane fit along the beam. The grayed ellipse represents the image-plane position of the afterglow 207 days post-merger that was obtained in G19 and used in M22. All data are in the HSA frame and are relative to the HSA observations’ phase center (denoted by a star).