First results of VSOP imaging of strong GPS sources

We are using the VSOP spacecraft, HALCA, together with ground-based telescopes, to image six strong GPS sources with compact double structure. Space-ground baselines are needed to achieve the resolution to accurately measure component sizes at the frequency of the spectral peak, an essential requirement in distinguishing between free-free and synchrotron self absorption emission mechanisms. Many of the components of these sources are only just beginning to show signs of any internal structure on the longest Earth baselines and space VLBI is the only technique that permits investigation of their most compact structure at the frequency of the spectral peak.