ACCURATE REGISTRATION OF RADIO AND OPTICAL-IMAGES OF SN 1987A

We present precision astrometry of the supernova 1987A which, for the first time, accurately registers high-resolution optical and radio images to better than 100 milliarc-second (mas). We have used preliminary results from the Hipparcos satellite, along with astrometric photographic plates, to redetermine the optical position of SN 1987A, and have made VLBI observations of radio stars to link the Hipparcos and VLBI reference frames in the vicinity of SN 1987A. This has allowed us to register the optical and radio images with an accuracy of similar to 70 mas. We find that the centre of the radio emission coincides with the position of the optical star at the centre of SN 1987A much more closely than previously found and conclude that the radio emission is due to interaction between an expanding shock front and the surrounding medium. However, a marginally significant displacement of the radio emission towards the east (140 mas) may indicate that the shock wave has expanded asymmetrically.