CHAPTER THREE
Intra-Day Variability, Gravitational Lensing and
Polarization
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, RADIO INTRA-DAY VARIABILITY: ANSWERS AND QUESTIONS
DAVID L. JAUNCEY
Australia Telescope National Facility, CSIRO, Australia E-mail:
LUCYNA KEDZIORA-CHUDCZER
Australia Telescope National Facility, and Anglo-Australian Observatory, Epping NSW, Australia
E-mail:
JAMES E.J. LOVELL
Australia Telescope National Facility, CSIRO, Australia; E-mail:
JEAN-PIERRE MACQUART
RCfTA, School of Physics, University of Sydney, NSW, Australia; E-mail:
GEORGE D. NICOLSON
Harteheesthoek Radio Astronomy Observatory, Krugersdorp, South Africa
E-mail: george @ hartrao. ac. z,a
RICK A. PERLEY
National Radio Astronomy Observatory, Socorro, NM, U.S.A.; E-mail:
JOHN E. REYNOLDS
Australia Telescope National Facility, CSIRO, Australia; E-mail:
ANASTASIOS K. TZIOUMIS
Australia Telescope National Facility, CSIRO, Australia; E-mail:
MARK H. WIERINGA
Australia Telescope National Facility, CSIRO, Australia; E-mail:
HAYLEY E. BIGNALL
Department of Physics and Mathematical Physics, University of Adelaide, SA, Australia
E-mail: hbignall®physics.adelaide.edu.au
Abstract. 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 10 to
102' K are encountered if the IDV is intrinsic to the source. We discuss here the accumulating evid-
ence 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.
1. Introduction
Since its discovery (Dent, 1965) the radio variability of extragalactic radio sources
has been a powerful indicator of the presence of compact source structure. Several
Astrophysics and Space Science 278: 87-92, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
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Intra-Day Variability, Gravitational Lensing and
Polarization
Downloaded from https://www.cambridge.org/core. IP address: 34.228.24.229, on 23 May 2020 at 17:51:59, subject to the Cambridge Core terms of
use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100000750
, RADIO INTRA-DAY VARIABILITY: ANSWERS AND QUESTIONS
DAVID L. JAUNCEY
Australia Telescope National Facility, CSIRO, Australia E-mail:
LUCYNA KEDZIORA-CHUDCZER
Australia Telescope National Facility, and Anglo-Australian Observatory, Epping NSW, Australia
E-mail:
JAMES E.J. LOVELL
Australia Telescope National Facility, CSIRO, Australia; E-mail:
JEAN-PIERRE MACQUART
RCfTA, School of Physics, University of Sydney, NSW, Australia; E-mail:
GEORGE D. NICOLSON
Harteheesthoek Radio Astronomy Observatory, Krugersdorp, South Africa
E-mail: george @ hartrao. ac. z,a
RICK A. PERLEY
National Radio Astronomy Observatory, Socorro, NM, U.S.A.; E-mail:
JOHN E. REYNOLDS
Australia Telescope National Facility, CSIRO, Australia; E-mail:
ANASTASIOS K. TZIOUMIS
Australia Telescope National Facility, CSIRO, Australia; E-mail:
MARK H. WIERINGA
Australia Telescope National Facility, CSIRO, Australia; E-mail:
HAYLEY E. BIGNALL
Department of Physics and Mathematical Physics, University of Adelaide, SA, Australia
E-mail: hbignall®physics.adelaide.edu.au
Abstract. 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 10 to
102' K are encountered if the IDV is intrinsic to the source. We discuss here the accumulating evid-
ence 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.
1. Introduction
Since its discovery (Dent, 1965) the radio variability of extragalactic radio sources
has been a powerful indicator of the presence of compact source structure. Several
Astrophysics and Space Science 278: 87-92, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Downloaded from https://www.cambridge.org/core. IP address: 34.228.24.229, on 23 May 2020 at 17:51:59, subject to the Cambridge Core terms of
use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100000750
