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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.