Ghosh, T. ; Gopal-Krishna, (1990) A multifrequency study of radio intensity variations for active galactic nuclei of different optical classes Astronomy & Astrophysics, 230 (2). pp. 297-303. ISSN 0004-6361
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Official URL: http://adsabs.harvard.edu/abs/1990A&A...230..297G
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: | Article |
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Source: | Copyright of this article belongs to EDP Sciences. |
ID Code: | 76487 |
Deposited On: | 02 Jan 2012 13:30 |
Last Modified: | 04 Jan 2012 15:43 |
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