Abstract: Cygnus A is the archetypal high luminosity
radio galaxy. It is one of the most powerful radio galaxies known,
and, at z=0.056, is located extraordinarily close to us. The source is
at the center of a dense, highly magnetized X-ray emitting cluster,
which has evidently retarded the expansion of its radio lobes,
resulting in unusually high surface brightness. The combination of
this high brightness and proximity makes this source an ideal
candidate for detailed radio imaging studies. Early VLA observations,
taken from the late 1970s through the early 1990s, demonstrated the
presence of relativistic jets, an extraordinarily high rotation
measure (RM) screen with well-defined large-scale structure, and an
apparent lack of depolarization on ~0.5 arcsecond (500 pc) scale at
6cm wavelength.
The Jansky Very Large Array (JVLA) offers unprecedented and unequalled
high-sensitivity, high-resolution, wideband imaging capabilities. An
extensive observing program, spanning 2 through 18 GHz, with all four
configurations, was executed in 2014-2015, with a key goal of
determining the internal thermal gas density within the radio lobes,
utilizing the depolarization characteristics of the source
emission. The new data show a complex and multi-varied depolarization
structure, which has so far defied simple, unique explanations.
But perhaps more interesting than the polarimetry and imaging are
discoveries resulting from the new data which were not anticipated by
the proposers: (i) A weak (~5 mJy) transient offset from the Cygnus A
nucleus by 0.4 arcseconds (~400 pc) of extraordinarily small angular
scale (~0.1 mas ~ 0.1 pc at the distance of Cygnus A), and (ii) an
elliptical, small (100 -- 200 parsec) flat-spectrum, emission region
centered on the nucleus, and oriented perpendicularly to the radio
jets, with brightness temperature ~700 K. The characteristics are
consistent with an ionized gas torus surrounding the nucleus.
In this colloquium, I will discuss our interpretations of these new
results, and emphasize the importance of careful, human, examination
of new and deep observations. If time permits, I will breifly review
the NRAO's plans for building a 'Next-Generation Very Large Array'.
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