Probing the innermost regions of AGN jets and their magnetic fields with
  RadioAstron. III. Blazar S5 0716+71 at microarcsecond resolution
  We present RadioAstron Space VLBI imaging observations of the BL Lac object
S5 0716+71 made on January 3-4 2015 at a frequency of 22 GHz (wavelength
$\lambda=1.3$ cm). The observations were made in the framework of the AGN
Polarization Key Science Program. The source was detected on projected
space-ground baselines up to 70 833 km (5.6 Earth diameters) for both, parallel
hand and cross-hand interferometric visibilities. We have used these detections
to obtain a full-polarimetric image of the blazar at an unprecedented angular
resolution of 24 $\mu$as, the highest for this source to date. This enabled us
to estimate the size of the radio core to be $<12\times5~\mu$as and to reveal a
complex structure and a significant curvature of the blazar jet in the inner
100 $\mu$as, which is an indication that the jet viewing angle lies inside the
opening angle of the jet conical outflow. Fairly highly (15%) linearly
polarized emission is detected in a jet region of 19 $\mu$as in size, located
58 $\mu$as downstream from the core. The highest brightness temperature in the
source frame is estimated to be $>2.2\times10^{13}$ K for the blazar core. This
implies that the inverse Compton limit must be violated in the rest frame of
the source, even for the largest Doppler factor $\delta\thicksim25$ reported
for 0716+714.
