J0316+4328: a probable ‘asymmetric double’ lens

We report a probable gravitational lens J0316+4328, one of 19 candidate asymmetric double lenses (two images at a high flux density ratio) from CLASS. Observations with the Very Large Array (VLA), MERLIN and the Very Long Baseline Array (VLBA) imply that J0316+4328 is a lens with high confidence. It has two images separated by 0.40 arcsec, with 6-GHz flux densities of 62 mJy and 3.2 mJy. The flux density ratio of ∼19 (constant over the frequency range 6–22 GHz) is the largest for any two-image gravitational lens. High-resolution optical imaging and deeper VLBI maps should confirm the lensing interpretation and provide inputs to detailed lens models. The unique configuration will give strong constraints on the lens galaxy's mass profile.