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Paper: Multi-Frequency & Multi-Epoch VLBI Study of Cygnus A
Volume: 340, Future Directions in High Resolution Astronomy: The 10th Anniversary of the VLBA
Page: 30
Authors: Bach, U.; Kadler, M.; Krichbaum, T.P.; Middelberg, E.; Alef, W.; Witzel, A.; Zensus, J.A.
Abstract: We present the first multi-frequency phase-referenced observations of Cygnus A done with the VLBA at 15 and 22GHz. We find a pronounced two-sided jet structure, with a steep spectrum along the jet and a highly inverted spectrum towards the counter-jet. The inverted spectrum and the frequency dependent jet to counter-jet ratio suggest an obscuring torus in front of the counter-jet. From 14 epochs of 15GHz VLBA data we accurately derive the jet and counter-jet kinematics. For the inner jet (r ≤ 5 mas) we measure motions of βapp ≈ 0.2 − 0.5 h−1 and on the counter-jet side we find βapp ≈ 0.03 ± 0.02 h−1. We discuss the jet velocities within the unified jet model.
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