The jet of S5 0716+71 at $\mu$as scales with RadioAstron

Abstract

Ground-space interferometer RadioAstron provides unique opportunity to probe detail structure of the distant active galactic nuclei at $\mu$as 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 $57\times 24\mu$as. It reveals complex structure of the blazar jet in the inner 100 $\mu$as, 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 $\ge 2.2\times 10^{13}$ K is in excess of theoretical limits, suggesting the physical conditions are far from the equipartition between relativistic particles and magnetic field.

11 pages, 4 figures; Unedited, Advances in Space Research, in press; Proceedings of the COSPAR 2018 42nd Assembly (Pasadena, CA, July 14-22 2018)