Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....108...64c&link_type=abstract
The Astronomical Journal, vol. 108, no. 1, p. 64-75
Astronomy and Astrophysics
Astrophysics
26
Cygnus Constellation, Radio Galaxies, Radio Jets (Astronomy), Radio Sources (Astronomy), Very Long Base Interferometry, Astrophysics, Radio Astronomy, Radio Emission
Scientific paper
We present an image of the core and nuclear jet in Cygnus A at 5 GHz with a resolution of approximately 1 mas, obtained from 'global array' MKIIIA very long base interferometry (VLBI) observations. Comparison of this image (epoch 1991.44) with a previous image made using similar techniques (epoch 1986.89) reveals outward motion of the brighter features in the jet between epochs. The allowed range in velocity for the brightest feature in the jet is: 0.19 c h-1 to 0.48 c h-1. The peak surface brightness and total flux density of the core and jet have varied less than 10% between epochs, although individual knots may have varied by as much as 40%. The pc-scale jet is aligned with the kpc-scale jet to within 2 deg. The core is self-absorbed, with a steeply rising spectrum of index greater than or equal to 0.9 between 5 and 43 GHz. The counterjet in Cygnus A remains elusive. From a combined epoch image we determine a nominal 'best' range for the jet to counterjet flux density ratio of: 8 less than or equal to R less than or equal to 21, with a firm lower limit being: R greater than or equal to 5, as dictated by extensive analysis of 'simulated' data sets. In the context of the twin-symmetric relativistic jet model for powerful radio galaxies and quasars, the conclusions are that the Cygnus A jet must be at an intermediate angle relative to our line of sight (between 11 deg and 60 deg), and must be moving at an intermediate velocity (between 0.37 and 0.74 times the speed of light).
Bartel Norbert
Carilli Christopher L.
Diamond Phillip
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