The jet of S5 0716[formula omitted]71 at [formula omitted]as scales with RadioAstron

Abstract

Ground-space interferometer RadioAstron provides unique opportunity to probe detail structure of the distant active galactic nuclei at μas scales. Here we report on RadioAstron observations of the BL Lac object S5 0716+71, performed in a framework of the AGN Polarization and Survey Key Science Programs at 22 GHz during 2012–2018. We obtained the highest angular resolution image of the source to date, at 57×24μas. It reveals complex structure of the blazar jet in the inner 100 μas, with emission regions that can be responsible for the blazar variability at timescales of a few days to week. Linear polarization is detected in the core and jet areas at the projected baselines up to about 5.6 Earth diameters. The observed core brightness temperature in the source frame of ⩾2.2×1013 K is in excess of theoretical limits, suggesting the physical conditions are far from the equipartition between relativistic particles and magnetic field.