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The Variability of a Large Sample of Quasars

from V - Beams, Jets and Blazars

Published online by Cambridge University Press:  04 August 2010

I. M. Hook
Affiliation:
Institute of Astronomy, Madingley Road, Cambridge, CB3OHA
R. G. McMahon
Affiliation:
Institute of Astronomy, Madingley Road, Cambridge, CB3OHA
B. J. Boyle
Affiliation:
Institute of Astronomy, Madingley Road, Cambridge, CB3OHA
M. J. Irwin
Affiliation:
Royal Greenwich Observatory, Madingley Road, Cambridge, CB3 0EZ
Andrew Robinson
Affiliation:
University of Cambridge
Roberto Juan Terlevich
Affiliation:
Royal Greenwich Observatory, Cambridge
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Summary

Abstract

The variability properties of a sample of over 300 optically–selected quasars near the South Galactic Pole (SGP) have been studied using a series of eleven UKST Bj plates at seven epochs, spanning 16 years. Quasars of high luminosity show significantly less variation than those with low luminosity. A similar, though much weaker, trend with redshift was found; lower redshift quasars varying proportionally more than high redshift quasars. The observed trends are a consequence of an intrinsic dependence of quasar variability on luminosity combined with the effects of time–dilation and have strong implications for quasar samples selected solely on variability.

Introduction

Variability provides a simple yet powerful means for investigating the physical processes at work in the inner regions of AGN. The primary diagnostics for optical variability are: the dependence on absolute magnitude and redshift, the timescale of variations in the quasar rest frame and the degree of coherence of individual quasar light curves — in our case taken as an ensemble. In addition to providing insight into quasar models an important feature of such a study is the ability to predict selection effects for quasar samples chosen purely on the basis of variability (e.g., Hawkins 1986). In this paper we summarise our method and results: a more detailed account is given in Hook et al. (1991) and Hook et al. (1992).

Data

The sample of quasars was taken principally from the catalogue of Hewitt & Burbidge (1989) with additional objects from other surveys.

Type
Chapter
Information
The Nature of Compact Objects in Active Galactic Nuclei
Proceedings of the 33rd Herstmonceux Conference, held in Cambridge, July 6-22, 1992
, pp. 416 - 419
Publisher: Cambridge University Press
Print publication year: 1994

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