Role of the companion lensing galaxy in the CLASS gravitational lens
  B1152+199
  We reinvestigate the Cosmic Lens All-Sky Survey (CLASS) gravitational lens
B1152+199 using archived Hubble Space Telescope (HST) data and Very Long
Baseline Interferometry (VLBI) data. A consistent luminosity ratio within
effective radius between the host galaxy and the X-galaxy is measured from HST
tri-band images, which leads to a mass ratio between the two galaxies as
$r_b\sim 2$. To determine the role of the X-galaxy in the lens system, we
modelled the dual-lens system with constraints from the VLBI-resolved jet
components and the HST images. The 8.4-GHz global-VLBI data currently provide
the most stringent constraints to the mass model, especially to the radial
power-law slope. The optimized models for this two-image three-component radio
lens favour a steeper-than-isothermal inner slope. The jet bending in image B
was also investigated and it turned out to be rather a misalignment than a
curvature. The goodness of fit indicates that the role of the X-galaxy is
crucial in the lens system if three pairs of resolved jet components are to be
fitted. When we imported the optimal model from radio constraints to optical
modelling with the HST tri-band data, the optimization kept the consistency of
the optimal model and successfully reproduced the features observed in the HST
images. This implies that the diffuse emission discovered in the HST images is
actually a detection of the secondary lensing effects from the companion lens.
