Abstract
Many extragalactic radio sources exhibit radio structures with some degree of rotational symmetry1,2, which in extreme cases (for example, 3C315 (ref. 3) and NGC326 (ref. 4)) suggests precession of the source axis, such as might result if a relativistic beam of particles5,6 or stream of plasmoids7 were to change its orientation during the source lifetime1. In such circumstances we might expect radiative and other energy losses to steepen the spectrum of the older regions of emission8 away from the current sites of activity, and so make them more prominent on low-frequency maps of the source structure. The new multi-telescope radio-linked interferometer (MTRLI)9 at Jodrell Bank was used during January and February 1980 at a frequency of 408 MHz to map the extragalactic radio sources 3C196 and 3C305 with a resolution of ∼1 arc s. We show here that both the markedly symmetric structures observed and the spectral index distributions inferred from comparison with previously published 5-GHz maps10 provide evidence for the source axes having rotated during the lifetime of the emitting regions.
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Lonsdale, C., Morison, I. Rotationally symmetric structure in two extragalactic radio sources. Nature 288, 66–69 (1980). https://doi.org/10.1038/288066a0
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DOI: https://doi.org/10.1038/288066a0
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