DEPOLARIZATION AND OTHER ASYMMETRIES IN DOUBLE RADIO-SOURCES

The presence of a one-sided jet in double radio sources is often interpreted as an orientation effect due to relativistic beaming. The counterjet side is more depolarized, consistent with a larger path-length through a depolarizing medium. I consider this and other asymmetries in detail. The polarization curves of a small sample are shown to be consistent with the expected behaviour of a source behind a partially resolved foreground screen. I model the depolarization asymmetry and show how the orientation angles of the sources can be found. There is a deficit of sources in the plane of the sky for the Garrington et al. sample, although this may be a selection effect. Depolarization is only correlated with arm-length for sources close to the plane of the sky, such as radio galaxies. I show that the recently observed spectral index asymmetry can also be interpreted as an orientation effect if the hotspots advance at speeds of v almost-equal-to 0.2c. This supports the idea that double sources are intrinsically two-sided and that the depolarization and spectral asymmetries are primarily due to orientation. High flow velocities in the hotspots give a natural explanation for the compactness asymmetry, and imply a spectral index asymmetry for the hotspots themselves.