A pulsar wind nebula (PWN, plural PWNe), sometimes called a plerion (derived from the Greek "πλήρης", ''pleres'', meaning "full"),
is a type of
nebula sometimes found inside the shell of a
supernova remnant
A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...
(SNR), powered by winds generated by a central
pulsar. These nebulae were proposed as a class in 1976 as enhancements at
radio wavelengths inside supernova remnants.
They have since been found to be infrared, optical, millimetre,
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
and
gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
sources.
Evolution of pulsar wind nebulae
Pulsar wind nebulae evolve through various phases.
New pulsar wind nebulae appear soon after a pulsar's creation, and typically sit inside a
supernova remnant
A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...
, for example the
Crab Nebula,
or the nebula within the large
Vela Supernova Remnant
__NOTOC__
The Vela supernova remnant is a supernova remnant in the southern constellation Vela. Its source Type II supernova exploded approximately 11,000–12,300 years ago (and was about 800 light-years away). The association of the Vela super ...
.
As the pulsar wind nebula ages, the supernova remnant dissipates and disappears. Over time, pulsar wind nebulae may become
bow-shock nebulae surrounding millisecond or slowly rotating pulsars.
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 that are generated by the spinning pulsar. The pulsar wind often streams into the surrounding interstellar medium, creating a standing
shock wave
In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...
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 astronomy, the spectral index of a source is a measure of the dependence of radiative flux density (that is, radiative flux per unit of frequency) on frequency. Given frequency \nu and radiative flux density S_\nu, the spectral index \alpha is g ...
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.
See also
*
3C 58
3C 58 or 3C58 is a pulsar (designation PSR J0205+6449) and supernova remnant ( pulsar wind nebula) within the Milky Way that is possibly associated with the supernova of 1181. There are, however, signs that indicate that it could be seve ...
*
G292.0+01.8
*
Crab Nebula
References
External links
The Pulsar Wind Nebula Catalog
{{DEFAULTSORT:Pulsar Wind Nebula
Supernova remnants
Wind nebula
Nebulae
Wind nebula