A Multi frequency study of Radio Intensity Variations For Active Galactic Nuclei of Different Optical Classes

Ghosh, T and Gopalakrishna, * (1990) A Multi frequency study of Radio Intensity Variations For Active Galactic Nuclei of Different Optical Classes. In: Astronomy & Astrophysics, 230 (2). pp. 297-303.

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Abstract

A study of radio intensity variations at seven frequencies in the range 0.3 to 90 GHz for compact extragalactic radio sources classified as BL Lacs and high- and low-optical polarization quasars (HPQs and LPQs) is presented. This include the results of flux-density monitoring of 33 compact sources for three years at 327 MHz with the Ooty Synthesis Radio Telescope. The degrees of 'short-term' (tau less than about 1 yr) variability for the three optical types are found to be indistinguishable at low frequencies (less than 1 GHz), pointing to an extrinsic origin for the low-frequency variability. At high frequencies, a distinct dependence on optical type is present, the variability increasing from LPQs, through HPQs to BL Lacs. This trend persists even when only sources with ultra-flat radio spectra (alpha greater than -0.2) are considered. Implications of this for the phenomenon of high-frequency variability and the proposed unification schemes for different optical types of active galactic nuclei are discussed.

Item Type:	Journal Article
Publication:	Astronomy & Astrophysics
Publisher:	EDP Sciences
Additional Information:	Copyright of this article belongs to EDP Sciences.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	06 Jan 2011 12:21
Last Modified:	06 Jan 2011 12:21
URI:	http://eprints.iisc.ac.in/id/eprint/34871

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