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

TL;DR

This study uses RadioAstron space VLBI data to measure extremely high brightness temperatures in quasar B0529+483, revealing the effects of interstellar scattering and implications for the quasar's physical conditions.

Contribution

It provides the first detailed analysis of scattering effects and brightness temperatures in B0529+483 at multiple frequencies, advancing understanding of AGN core physics.

Findings

Brightness temperatures exceed 10^13 K at 4.8 and 22 GHz.

Two characteristic angular scales identified: ~100 μas and ~10 μas.

Evidence of scattering substructure affecting measurements.

Abstract

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.