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Radio Intra-Day Variability: Answers and Questions

Published online by Cambridge University Press:  12 April 2016

David L. Jauncey ,
Lucyna Kedziora-Chudczer ,
James E.J. Lovell ,
Jean-Pierre MacQuart ,
George D. Nicolson ,
Rick A. Perley ,
John E. Reynolds ,
Anastasios K. Tzioumis ,
Mark H. Wieringa  and
Hayley E. Bignall
David L. Jauncey
Affiliation:
Australia Telescope National Facility, CSIRO, Australia. E-mail: djauncey@atnf.csiro.au
Lucyna Kedziora-Chudczer
Affiliation:
Australia Telescope National Facility, and Anglo-Australian Observatory, Epping NSW, Australia. E-mail: lkedzior@atnf.csiro.au
James E.J. Lovell
Affiliation:
Australia Telescope National Facility, CSIRO, Australia. E-mail: jlovell@atnf.csiro.au
Jean-Pierre MacQuart
Affiliation:
RCfTA, School of Physics, University of Sydney, NSW, Australia. E-mail: jpm@physics.usyd.edu.au
George D. Nicolson
Affiliation:
Harteheesthoek Radio Astronomy Observatory, Krugersdorp, South Africa. E-mail: george@hartrao.ac.za
Rick A. Perley
Affiliation:
National Radio Astronomy Observatory, Socorro, NM, U.S.A.. E-mail: rperley@nrao.edu
John E. Reynolds
Affiliation:
Australia Telescope National Facility, CSIRO, Australia. E-mail: jreynold@atnf.csiro.au
Anastasios K. Tzioumis
Affiliation:
Australia Telescope National Facility, CSIRO, Australia. E-mail: atzioumi@atnf.csiro.au
Mark H. Wieringa
Affiliation:
Australia Telescope National Facility, CSIRO, Australia. E-mail: mwiering@atnf.csiro.au
Hayley E. Bignall
Affiliation:
Department of Physics and Mathematical Physics, University of Adelaide, SA, Australia. E-mail: hbignall@physics.adelaide.edu.au

Abstract

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Intra-day variability (IDV) of active galactic nuclei (AGN) has been detected from gamma-ray energies to radio wavelengths. At high energies, such variability appears to be intrinsic to the sources themselves. However, at radio wavelengths, brightness temperatures as high as 1018 to 1021 K are encountered if the IDV is intrinsic to the source. We discuss here the accumulating evidence showing that, at radio wavelengths where the highest brightness temperatures are encountered, interstellar scintillation (ISS) is the principal mechanism causing IDV. While ISS reduces the implied brightness temperatures, they still remain uncomfortably high.

Type
Chapter Three Intra-Day Variability, Gravitational Lensing and Polarization
Information
International Astronomical Union Colloquium , Volume 182: Sources and Scintillations: Refraction and Scattering in Radio Astronomy , 2001 , pp. 86 - 92
Copyright
Copyright © Kluwer 2001

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