A new radio double lens from CLASS: B1127+385

We present the discovery of a new gravitational lens system with two compac t radio images separated by 0.701 +/- 0.001 arcsec, The lens system was dis covered in the Cosmic Lens All Sky Survey (CLASS) as a flat-spectrum radio source. Both radio components show structure in a Very Long Baseline Array (VLBA) 8.4-GHz radio image. No further extended structure is seen in Very L arge Array (VLA), Multi-Element Radio Linked Interferometer Network (MERLIN ) or VLBA images, Hubble Space Telescope (HST) WFPC2 images in F555W and F8 14W show two extended objects close to the radio components, which we ident ify as two lens galaxies, Their colours and mass-to-light ratios seem to fa vour two late-type spiral galaxies at relatively high redshifts (z(d) great er than or similar to 0.5). Faint emission is also detected at positions co rresponding to the radio images, A two-lens mass model can explain the observed VLBA structure. The best-fit ting model has a reduced chi(2) of 1.1. The relative positions of the VLBA subcomponents are reproduced within 0.08 mas, and the flux density ratios w ithin 20 per cent. We also reproduce the position angle and separation of t he two VLBA subcomponents in A and B within the observational errors, which we consider strong evidence for the validity of the lens model. Moreover, we find a surface density axis ratio of 0.74(-0.12)(+0.10) for the primary lens (G1), consistent with the surface brightness axis ratio of 0.69 +/- 0. 15. Also, the surface density position angle of (4.9(-22.4)(+28.2))degrees of G1 compares well with the (-6 +/- 13)degrees position angle of the surfa ce brightness distribution. The errors indicate the 99 per cent confidence interval.