A pulsar wind nebula (also known as "plerion", derived from Ancient Greek "pleres" meaning "full"?a term coined by Weiler & Panagia (1978)) is a nebula powered by the pulsar wind of a pulsar. At the early stage of their evolution, pulsar wind nebulae are often found inside the shells of supernova remnants. A prototypical pulsar wind nebula is the Crab Nebula.

The pulsar wind is streaming into the ambient medium and creating a standing shock, where it is decelerated to sub-relativistic speed. Beyond this radius synchrotron emission increases in the magnetized flow.

Pulsar wind nebulae often show the following properties:

• An increasing brightness towards the center, without a shell-like structure.
• A highly polarized flux and a flat radio spectral index, ?=0-0.3. The index steepens at X-ray energies due to synchrotron and radiation losses and on the average has an X-ray photon index of 1.3-2.3.
• An X-ray size that is generally smaller than their radio and optical size (due to smaller synchrotron lifetimes of the higher-energy electrons) (Safi-Harb 2004).
• A photon index at TeV gamma-ray energies of ~2.3.

Plerions can be powerful probes of a pulsar's interaction with its surroundings — their properties can be used to infer the geometry, energetics, and composition of the pulsar wind, the space velocity of the pulsar itself, and the properties of the ambient medium (Gaensler 2000).

See also

• The Pulsar Wind Nebula Catalog
• SNR G292.0+01.8

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