Motion of quasar images by gravitational lens galaxies

Rotational motions of twin quasar images due to the motion of a gravitational lens galaxy are studied. A weak gravity field and a point mass lens are assumed. Twin images of a quasar appear and rotate when a lens galaxy passes near a straight line connecting the observer with the quasar. The positions and velocities of the quasar images are calculated using various sets of parameters.Conclusions: (1) Quasar images move a few hundred milli-arc-seconds per year or more, if the lens galaxy passes within a thousandth parsec from the line connecting the observer with the quasar, (2) the distance between the galactic center and the quasar images is about ten kilo-parsec at the most.As an example, the velocities of 0957+561 A, B1 and B2 are calculated. Even the fastest case, they are 1.5, 1.8, and 1.6×10^–5 milli-arc-second per year, respectively.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.