A GRAVITATIONALLY-LENSED RING IN MG 1549+3047

We report the discovery of a new gravitational lens in the radio source MG 1549 + 3047. The source has a compact core and two lobes, with a faint optical counterpart to the core. The brighter lobe is shaped like a ring, and centered on a foreground galaxy with known redshift. The radio structure of the ring can be reproduced by distorting a typical radio lobe through a simple elliptical gravitational lensing potential, which models the mass distribution in the foreground galaxy. From a preliminary lens model, we show that the mass distribution follows the observed luminosity, and we predict a central velocity dispersion of about 230 km s-1. This corresponds to a blue mass-to-light ratio of about 18h solar units. The lens appears to be an ordinary elliptical galaxy, and the many multiply-imaged structures make MG 1549 + 3047 well-suited to directly determine its mass distribution.