VLBI observations of eight extreme scattering event sources: Milliarcsecond-scale structure

We present multiple-epoch, multiple-frequency VLBI observations of eight extragalactic sources whose radio light curves have undergone an extreme scattering event (ESE). The VLBI observations were made at times during which the sources were not undergoing ESE events. The eight sources show relatively simple intrinsic structure, with one or two dominant components containing the majority of the total flux density, and component angular sizes on the order of several milliarcseconds. We have interpreted the ESE light curves for these sources in the context of a simple statistical scattering model. There appears to be no direct correspondence between intrinsic source structure and the form of the radio light curves during an ESE. Our results suggest that some of the variations in the radio light curves of these sources are due to the complexity of the scattering medium itself.