The high brightness temperature of B0529+483 revealed by RadioAstron and
  implications for interstellar scattering
  The high brightness temperatures, $T_\mathrm{b}\gtrsim 10^{13}$ K, detected
in several active galactic nuclei by RadioAstron space VLBI observations
challenge theoretical limits. Refractive scattering by the interstellar medium
may affect such measurements. We quantify the scattering properties and the
sub-mas scale source parameters for the quasar B0529+483. Using RadioAstron
correlated flux density measurements at 1.7, 4.8, and 22 GHz on projected
baselines up to 240,000 km we find two characteristic angular scales in the
quasar core, about 100 $\mu$as and 10 $\mu$as. Some indications of scattering
substructure are found. Very high brightness temperatures, $T_\mathrm{b}\geq
10^{13}$ K, are estimated at 4.8 GHz and 22 GHz even taking into account the
refractive scattering. Our findings suggest a clear dominance of the particle
energy density over the magnetic field energy density in the core of this
quasar.
