1ST-EPOCH AND 2ND-EPOCH VLBI OBSERVATIONS OF THE GRAVITATIONAL LENS SYSTEM 2016+112

Two 18 cm Mark III VLBI observations of the 2016 + 112 gravitational lens system indicate that A and B have structure at the milliarcsecond level. Neither A nor B can be described with only one component. The detailed brightness distributions for A and B are not uniquely determined, however, because of sparse sampling and low signal-to-noise ratios. Many models are considered. One hypothesis consistent with all of the models is that images A and B are not related by linear magnification because the source is evolving on a time scale comparable to or shorter than the time delay between images. Models not required to be consistent with linear magnification were not. Models required to be consistent with linear magnification either fitted the data significantly less well or indicated significantly different matrices for the two epochs. The lens is a large structure consisting of at least two galaxies, so it is unlikely that the magnification matrix would change significantly in the 5.5 years between observational epochs. Any given model shows evidence for source evolution between epochs, but the details of that source evolution are highly model-dependent. More definite conclusions could be made if the brightness distributions of A and B could be derived without ambiguity. Significantly better sampling with an order of magnitude more data are necessary, along with a better understanding of the error contributions.