If the characteristics of the emitted radiation do not depend on the temperature of the source, the radiation is known as 'non-thermal radiation'.
In astronomy, there are three common types of non-thermal radiation:

1. Synchrotron emission is generated by charged particles spiralling around magnetic field lines at relativistic speeds.
2. Compton scattering is the process in which electrons are effectively pushed around by high energy photons, which scatter off the electron after imparting some of their energy.
3. There is also stimulated emission, where electrons in a metastable state are prompted to decay to the ground state by a passing photon with the same energy as the difference between the two levels.