Space VLBI Observations Show Tb> 10 12 K in the Quasar NRAO 530

We present here space-based VLBI observations with VSOP and a southern hemisphere ground array of the gamma-ray blazar NRAO 530 at 1.6 GHz and 5 GHz. The brightness temperature of the core at 1.6 GHz is 5 × 10 K. The size is near the minimum observable value in the direction of NRAO 530 due to interstellar scattering. The 5 GHz data show a single component with a brightness temperature of ∼ 3 × 10 K, significantly in excess of the inverse Compton limit and of the equipartition brightness temperature limit (Readhead 1994). This is strong evidence for relativistic motion in a jet requiring model-dependent Doppler boosting factors in the range 6 to 60. We show that a simple homogeneous sphere probably does not model the emission region accurately. We favor instead an inhomogeneous jet model with a Doppler boosting factor of 15. Subject headings: radiation mechanisms: non-thermal — galaxies: active — galaxies: jets — techniques: interferometric