RadioAstron Early Science Program Space-VLBI AGN survey: strategy and
  first results
  RadioAstron is a project to use the 10m antenna on board the dedicated
SPEKTR-R spacecraft, launched on 2011 July 18, to perform Very Long Baseline
Interferometry from space - Space-VLBI. We describe the strategy and highlight
the first results of a 92/18/6/1.35cm fringe survey of some of the brighter
radio-loud Active Galactic Nuclei (AGN) at baselines up to 25 Earth diameters
(D_E). The survey goals include a search for extreme brightness temperatures to
resolve the Doppler factor crisis and to constrain possible mechanisms of AGN
radio emission, studying the observed size distribution of the most compact
features in AGN radio jets (with implications for their intrinsic structure and
the properties of the scattering interstellar medium in our Galaxy) and
selecting promising objects for detailed follow-up observations, including
Space-VLBI imaging. Our survey target selection is based on the results of
correlated visibility measurements at the longest ground-ground baselines from
previous VLBI surveys. The current long-baseline fringe detections with
RadioAstron include OJ 287 at 10 D_E (18cm), BL Lac at 10 D_E (6cm) and
B0748+126 at 4.3 D_E (1.3 cm). The 18 and 6cm-band fringe detections at 10 D_E
imply brightness temperatures of T_b ~ 10^13 K, about two orders of magnitude
above the equipartition inverse Compton limit. These high values of T_b might
indicate that the jet flow speed is often higher than the jet pattern speed.
