Debora Mary Katz-Stone

Determining the shape of spectra in extended radio sources

We present an innovative technique for determining the shape of the synchrotron spectra in extended radio sources. This method involves a three-frequency color-color diagram that emphasizes differences in the shapes of various theoretical models. The advantages of this technique over standard multifrequency mapping are that (1) it is easy to collect the necessary data (only three frequencies required), (2) it highlights the curvature changes in the spectrum, and (3) it puts data from all regions of the source onto one plane; and if a global spectrum exists, (4) it allows for effectively continuous sampling in frequency, (5) it provides sampling over a much larger range of electron energies, and (6) both the shape of the spectrum and the injection index, if it exists, can be determined by three-frequency data

Do Relativistic Electrons Either Gain or Lose Energy, Outside of Extragalactic Nuclei?

In the generally accepted models of high-luminosity extragalactic radio sources, the relativistic electron distribution evolves significantly outside of its source in the galactic nucleus; synchrotron losses occur throughout the source, and the harder (flatter) spectra seen in the hot spots are one indicator of relativistic particle acceleration. Our reanalysis and interpretation of the Carilli et al. (1991) data on Cygnus A, on the other hand, showed no evidence for evolution of the electron distribution function, and no evidence of the universally assumed injection power-law distribution. Having found a spectrum that describes an entire source, we have also introduced the technique of correcting synchrotron maps for frequency-dependent effects. In this way, a partial deconvolution of the underlying physical parameters is possible. In Cygnus A, this correction procedure led to the dominance of a hitherto unrecognized structure, an edge-brightened channel girdled by rings. We briefly discuss some implications of this work and our plans to continue this line of investigation. Subject headings: acceleration of particles — galaxies: individual (Cygnus A) — galaxies: nuclei — radiation mechanisms: nonthermal — radio continuum: galaxies

The quest for particle acceleration in extragalactic sources

In this paper, we discuss the types of observations used to study the acceleration of relativistic electrons in the diffuse plasma of extragalactic radio sources. The goal of this work is to identify the conditions under which such acceleration is important and which acceleration processes dominate. We identify some of the pitfalls in such analyses and suggest directions for future work.