Improper motions in lensed QSOs
Williams, L L R, Saha, P · CERN Document Server (European Organization for Nuclear Research) · 1995
We argue that individual images in multiple-image QSOs could easily have substructure at the level of 0.1'' (i.e., unresolvable even with HST); microlensing within such substructure would cause centroid shifts, observable even from the ground as pseudo proper motions. We present a model of the four-image system 2237+0305 in which Image B shows such ``improper motions" of order of 0.01'' over a few years.