Proper-motion of the X-ray emitting plasma. Red squares denote pixel with single photon events and black squares display double photon events. Left: X-ray emission (0.3−1.0 keV) from 2000 with Hα contours from 1997 in black. Right: X-ray emission from 2010 with Hα contours from 2008. The thick circles of radius coincide with the photon centroid, the thin circle indicates the position of the photons during the 2000 observation.