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Interpretation of Extreme Scattering Events

Published online by Cambridge University Press:  12 April 2016

Mark A. Walker
Mark A. Walker*
Affiliation:
Research Centre for Theoretical Astrophysics, School of Physics A28, University of Sydney, NSW 2006, Australia

Abstract

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Extreme Scattering Events are sometimes manifest in the light-curves of compact radio-quasars at frequencies of a few GHz. These events are not understood. The model which appears to offer the best explanation requires a new population of AU-sized, neutral gas clouds; these clouds would then make up a large fraction of the Galaxy’s dark matter. Independent of the question of which 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 below about 700 MHz. Consequently at these frequencies sources should typically manifest additional, faint images which are substantially delayed with respect to the primary image. Although some examples of 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.

Type
Chapter Four Extreme Scattering Events, Distribution of Material and IPS
Information
International Astronomical Union Colloquium , Volume 182: Sources and Scintillations: Refraction and Scattering in Radio Astronomy , 2001 , pp. 148 - 154
Copyright
Copyright © Kluwer 2001

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