The Diverse Properties of GPS Sources
  We discuss the morphology and kinematics of five gigahertz-peaked spectrum (GPS) sources that have been observed with the VLBA. We find a wide range of observed properties including core-jet structure, superluminal motion, variability, extended structure, and polarization, all of which appear to deviate from commonly-accepted GPS paradigms (e.g., O'Dea 1998). We suggest that the observed low frequency cutoff in GPS sources may be primarily due to free-free absorption rather than synchrotron self-absorption. 
M. L. Lister (NRAO), K. I. Kellermann (NRAO), I. I. Pauliny-Toth   (MPIfR)