INTERSTELLAR BROADENING OF IMAGES IN THE GRAVITATIONAL LENS PKS-1830-211

The remarkably strong radio gravitational lens PKS 1830-211 consists o f a 1 '' diameter Einstein ring with two bright compact (milliarcsecon d) components located on opposite sides of the ring, We have obtained 22 GHz Very Long Baseline Array (VLBA) data on this source in order to determine the intrinsic angular sizes of the compact components. Prev ious VLBI observations at lower frequencies indicate that the brightne ss temperatures of these components are significantly lower than 10(10 ) K (Jauncey et al.), less than is typical for compact synchrotron rad io sources and less than is implied by the short timescales of flux de nsity variations. A possible explanation is that interstellar scatteri ng is broadening the apparent angular size of the source and thereby r educing the observed brightness temperature, Our VLBA data support thi s hypothesis, At 22 GHz, the measured brightness temperature is at lea st 10(11) K, and the deconvolved size of the core in the southwest com pact component is proportional to v(-2) between 1.7 and 22 GHz. VLBI o bservations at still higher frequencies should be unaffected by inters tellar scattering.