2008 Supplement: Frascati Workshop 2007 / Beall

The Importance of Multifrequency Emission from Jets in Astrophysics

J. H. Beall


In this paper, I discuss some historical data on the radio and X-ray
variability of the active galaxy, Centaurus A (NGC 5128). The Cen A
data reviewed herein were the first detection of concurrent radio and
X-ray variability of an active galaxy. Such concurrent variability
demands that the radio and X-ray light originate from the same region in
the source, a result that allows us to further constrain the physical
parameters in the emitting region. The radio and X-ray data from Cen A
during this epoch bear a remarkable resemblence to both the radio data
from 3C120 (and other AGN) and the radio data from galactic
microquasars. The radio data for Cen A are not consistent with van der
Laan expansion, a circumstance reminiscent of some of the time
variability of the galactic microquasars. This suggests that concurrent,
spatially resolved data from multifrequency campaigns will be critical
to a refinement of source models for these objects, a result that
motivates some comments on what we mean by concurrent, spatially
resolved, multifrequency observations. Astrophysical jets are thus a
remarkable laboratory: They provide a confirmation of special
relativity in terms of relativistic Doppler boosting, superluminal
motion, and time dilation effects. When coupled with their black hole
neutron star origins, jets have implications for testing general
relativity. As our understanding of the ubiquity of the jet phonomena
has grown, we have been required to abandon the assumption of anisotropy
in the emitting region in most but not all cases.


astrophysical jets active galactic nuclei quasars microquasars

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