Class B1555+375: A new four-image gravitational lens system

We have discovered a new gravitational lens in the Cosmic Lens All-Sky Surv ey. The lens B1555 + 375 is a four-image system with a maximum separation o f 0." 42. VLA and MERLIN radio observations show these images in a characte ristic quadruple-lens configuration. Optical imaging with the Keck II Teles cope at R band shows a faint extended object. We estimate the combined emis sion from the lens and background source to be R = 25 mag. Observations at H band with the William Herschel Telescope also detected this extended obje ct. The combined lens and background source magnitude was measured to be H = 19 mag. Presently, redshifts for both the lensing galaxy and background s ource are undetermined. We conclude that one or more of the following are t rue: the lens galaxy is sub-L*, it has z > 0.5, or it is highly reddened. T he observed MERLIN component positions and flux densities can be well descr ibed by a lens model based on a singular isothermal ellipsoid mass distribu tion. Our best-fit lens model has a reduced chi(2) Of 2.6. High-resolution VLA radio observations should help to constrain the lens model further.