GB075

Ultra high resolution imaging of the archetypical radiogalaxy Cygnus

Abstract

Global VLBI observations at 7 mm allow to image Cygnus A with an observing beam
corresponding
to only ~280 Schwarzschild radii. With this unsurpassed spatial resolution, the fundamental
topic of relativistic jet launching and acceleration can be addressed, providing unique
observational tests for current MHD models on jet formation. Owing to the small viewing
angle, Doppler-boosting effects in CygA are minimal. This facilitates a direct measurement of
the jet-intrinsic speed. CygA is also one of the few radio galaxies where transverse resolution
studies are possible in both jet and counter-jet. In order to clarify the jet kinematic in the
presence of strong, but asymmetric velocity gradients,
and in view of velocity stratification due to instabilities, we propose to monitor CygA at 3
epochs. We complement this proposal by GMVA imaging at 86 GHz, for which we are
proposing in parallel. With accurate spectral index profiles we can locate the 'true' VLBI core
and test the thick torus, which is obscuring part of the counter-jet. Global VLBI at 7 mm can
probe the regions inside the inner edge of the donut-like absorber, allowing to measure its
geometry and derive some of its physical properties.

Investigators

Name	Institution
Tony Zensus	National Radio Astronomy Observatory; Max-Planck-Institut für Radioastronomie
Walter Alef	Max-Planck-Institut für Radioastronomie
Thomas Kirchbaum	Max-Planck-Institut für Radioastronomie
Uwe Bach *	Max-Planck-Institut für Radioastronomie
GBT Operator	Green Bank Observatory

* indicates the PI