VLBA snapshot imaging survey of scintillating sources

We present 8.4 GHz Very Long Baseline Array (VLBA) observations of 75 extragalactic radio sources drawn from the scintillating sources discovered in the Microarcsecond Scintillation-induced Variability survey. This survey clearly showed that the fraction of scintillating sources and the amplitude of their variability increases strongly with decreasing flux density, raising the possibility that scintillating sources may be systematically extremely core dominated. The observations presented here were designed to investigate this hypothesis. The results indeed show that most of the scintillating sources we observed with the VLBA have an extremely compact, core-dominated morphology, which has important implications for interpretations of the scintillation seen in these sources. In addition, these sources are potential candidates for inclusion in the International Celestial Reference Frame.