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Interpretation of Extreme Scattering Events

  • Mark A. Walker
Chapter
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Abstract

Extreme Scattering Events are sometimes manifest in the light-curves of compact radio-quasarsat frequencies of a few GHz. These events are not understood. The model which appears tooffer the best explanation requires a new population of AU-sized, neutral gas clouds; these cloudswould then make up a large fraction of the Galaxy’s dark matter. Independent of the question ofwhich theoretical model is correct, if we extrapolate the observed behaviour to low radio-frequencies,we expect that the sky should be criss-crossed by a network of narrow caustics, at frequencies belowabout 700 MHz. Consequently at these frequencies sources should typically manifest additional, faintimages which are substantially delayed with respect to the primary image. Although some examplesof this type of behaviour are already known, it is expected that these are just the tip of the iceberg,with strong selection biases having been imposed by the instrumentation employed to date.

Keywords

Optical Depth Column Density Angular Size Source Structure Lens Model 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media Dordrecht 2001

Authors and Affiliations

  • Mark A. Walker
    • 1
  1. 1.Research Centre for Theoretical Astrophysics, School of Physics A28University of SydneyAustralia

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