Multi-Frequency VLBI Observations of GHz-Peaked Spectrum Sources
  We report results of pentachromatic VLBI survey for 18 GHz-peaked spectrum sources. Spectral fitting at every pixel across five frequencies allows us to illustrate distribution of optical depth in terms of free-free absorption or synchrotron self absorption. Quasars and Seyfert 1 sources show one-sided morphology with a core at the end where the optical depth peaks. Radio galaxies and Seyfert 2 show symmetric double-sided jets with a optically thick core at the center. 
S. Kameno (1), M. Inoue (1), Z.-Q. Shen (2), S. Sawada-Satoh (3), K.   Wajima (4) ((1) National Astronomical Observatory of ...