Dual-frequency VLBI observations of the gravitational lens system PKS 1830-211

From simultaneous 8.4 and 2.3 GHz VLBA observations we have studied the morphology and properties of the compact components of the gravitational lens PKS 1830-211. We have found that the size of the southwest component increases as lambda(2), most probably due to scattering by interstellar plasma. while the size of the northeast component does not increase with such wavelength dependence, The small separation between both lensed components, compared with the typical size of scattering clumps in our Galaxy, suggests that the scattering material is located in the lensing galaxy, rather than in the Milky Way. Within the uncertainties, the flux-density ratios of the brightest feature in the two compact components for the two frequency bands agree with each other, as expected for images of the same background feature.