Laing-Garrington effect

In a DRAGN (a double radio source associated with an active galactic nucleus) in which there is a one-sided jet, or twin jets in which one is distinctly brighter than the other, the lobe containing the (brighter) jet is almost always less depolarized than the lobe on the other (counter-jet) side. This is known as the Laing-Garrington effect was was discovered Robert Laing and Simon Garrington in 1988 and can be explained neatly by unified schemes of DRAGNs.


The asymmetry between the two jets is caused by relativistic beaming, so the brighter jet is coming toward us and hence on the nearer side. The two lobes are embedded in the interstellar medium or halo of the host galaxy, and there is more of this material in front of the further lobe than the nearer. As the radio waves from the lobes travel through the intervening matter they are subjected to Faraday rotation that causes the depolarization. Hence the further lobe, on the counter-jet side, is more depolarized.