The high brightness temperature of B0529+483 revealed by RadioAstron and implications for interstellar scattering

Abstract

<p>The high brightness temperatures, Tb 1013 K, detected in several active galactic nuclei by<br />RadioAstron space VLBI observations challenge theoretical limits. Refractive scattering by<br />the interstellar medium may affect such measurements. We quantify the scattering properties<br />and the sub-mas scale source parameters for the quasar B0529+483. Using RadioAstron<br />correlated flux density measurements at 1.7, 4.8, and 22 GHz on projected baselines up to<br />240 000 km we find two characteristic angular scales in the quasar core, about 100 and 10 μas.<br />Some indications of scattering substructure are found. Very high brightness temperatures, Tb<br />≥ 1013 K, are estimated at 4.8 and 22 GHz even taking into account the refractive scattering.<br />Our findings suggest a clear dominance of the particle energy density over the magnetic field<br />energy density in the core of this quasar.<br />Key words: scattering – galaxies: jets – quasars: general – quasars: individual (B0529+483) –<br />radio continuum: galaxies.<br /></p>