The electromagnetic (EM) process are always related to photons because they are the particles to carry energy and momentum in electromagnetic interactions. Therefore, some of the EM reactions would GENERATE photons, such as pair annihilation , the inverse process of the pair creation. Electrons are also producing photons by interacting with magnetic field, which is called synchrotron radiation, the representative radiation process that can be described in the standard context of the classical electromagnetic theory.
Now let us derive the radiation intensity, i.e. the radiated energy per unit time . First we expand the treatment of the dipole radiation given by Eq. 8 to the super-relativistic condition that particles are moving almost at speed of light. The dipole is related to acceleration by and Eq. 8 gives the total radiation intensity as
In the uniform field, an electron's movement is characterized by the synchrotron frequency
Energies of the radiated photons are narrowly distributed around