Pulsar wind nebula

Properties of pulsar wind nebulae

Pulsar winds are composed of charged particles (plasma) accelerated to relativistic speeds by the rapidly rotating, hugely powerful magnetic fields above 1 teragauss (100 million teslas) that are generated by the spinning pulsar. The pulsar wind often streams into the surrounding interstellar medium, creating a standing shock wave called the 'wind termination shock', where the wind decelerates 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 as seen in supernova remnants.
• A highly polarized flux and a flat spectral index in the radio band, α=0–0.3. The index steepens at X-ray energies due to synchrotron radiation losses and on the average has an X-ray photon index of 1.3–2.3 (spectral index of 2.3–3.3).
• An X-ray size that is generally smaller than their radio and optical size (due to smaller synchrotron lifetimes of the higher-energy electrons).
• A photon index at TeV gamma-ray energies of ~2.3.

Pulsar wind nebulae can be powerful probes of a pulsar/neutron star's interaction with its surroundings. Their unique 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.