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Paper: Phase-Referencing on BL Lac
Volume: 386, Extragalactic Jets: Theory and Observation from Radio to Gamma Ray
Page: 279
Authors: Sokolov, A.; Cawthorne, T.
Abstract: We report results of a study designed to investigate a possible precession of the parsec-scale jet in BL Lac. The observations were conducted at 8, 15, 22, and 43 GHz and consist of seven epochs spanning about two years. We investigated the change in the absolute position of BL Lac’s radio core by means of phase-referencing with two nearby sources, 2151+431 and 2207+374. The shift in the position of the core perpendicular to the jet is a signature of precession. Periodic variations with an amplitude of ∼0.15 mas and a period of 1 year were found, but may be attributed to seasonal weather variations. We also detect a trend in position of the core at a rate of ∼0.1 mas over two years.
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