The optical appearance of the gravitational lens system B0218+35.7

Abstract

We present high-resolution CCD images (FWHM ≈ 0.6 – 0.7) of the compact gravitational lens system B0218+35.7 obtained at the Nordic Optical Telescope. Using aperture and point spread function photometry, we detect the two closely separated (335 mas) components A and B as well as the lensing galaxy. In the optical B seems to be very much brighter than A, in contrast to the radio structure. This suggests that most of the light from A is absorbed in the lensing galaxy, possibly by a giant molecular cloud located in the line of sight to component A. The lensing galaxy appears to be a late-type galaxy at a small inclination. For future variability studies, we present calibrated photometry of the system and its immediate surroundings, even though the relative faintness of A will make it difficult to obtain an optical time delay even with the Hubble Space Telescope.