synchrotron emission


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Synchrotron emission: (a) relativistic beaming (b) spectrum of synchrotron emissionclick for a larger image
Synchrotron emission: (a) relativistic beaming (b) spectrum of synchrotron emission

synchrotron emission

(sink -rŏ-tron) (synchrotron radiation; magnetobremsstrahlung) Electromagnetic radiation from very high energy electrons moving in a magnetic field. It is nonthermal emission and is also polarized (see polarization), usually strongly. It is the mechanism most often invoked to explain the radio emission from extragalactic radio sources and the emission from supernova remnants and pulsars.

When an electron moves in a magnetic field, it follows a circular path making ν = eB /2πm revolutions per second, where e and m are the electronic charge and mass and B is the magnetic flux density; ν is the gyrofrequency. The acceleration of the electron in its circular path causes it to radiate electromagnetic waves at frequency ν. This emission is called cyclotron radiation.

If the velocity of the electrons becomes comparable with the speed of light, the theory of relativity must be used to explain the observed phenomena. One effect is relativistic beaming in which the radiation is beamed forward in the direction of motion of the relativistic electron (see illustration (a)). The nature of the radiation changes from the simple cyclotron case and it becomes synchrotron emission. At low frequencies, the conditions in the source may cause the synchrotron emission to be reabsorbed before it can escape. The radio-source spectrum then exhibits a turnover, as is often seen in extragalactic radio sources (see illustration (b)). This is called synchrotron self-absorption. See also Razin effect.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
Mastichiadis, "Particle acceleration and synchrotron emission in blazar jets," Astronomy & Astrophysics, vol.
Analyzing the behavior of the photon index respect to the synchrotron lines of death, we determined the role of synchrotron emission inside the bursts.
However, from the absence of structure in 325 MHz maps of the NCP regions from the Westerbork Northern Sky Survey (WENSS, [26]), we were able to place a lower bound of [beta] > -2.2 on the spectral index of a single foreground, making synchrotron emission an untenable model for the 14.5 GHz signals, unless the fields happen to be associated with an active region where the normally steep synchrotron spectrum is kept unusually flat by the injection of high-energy electrons, for example, a supernova remnant that has undergone recent repowering (see for example [27]).
[34] proposed an alternative explanation of AME based on flat-spectrum synchrotron emission associated to star-forming regions to explain part of the WMAP first-year observations.
In Section 4, we consider a simple free-free and canonical synchrotron emission model for the thermal dust-subtracted microwave data.
They were correct to invoke so-called synchrotron emission for both the Cassiopeia A supernova remnant and the Cygnus radio galaxy.
Synchrotron emission results from cosmic-ray electrons accelerated in magnetic fields, and thus, depends on the energy spectrum of the electrons and the intensity of the magnetic field [49, 50].
Radio surveys at frequencies less than 2 GHz are dominated by synchrotron emission [52].

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