Color: energy spectra of the inverse Compton radiation of mono-energetic electrons upscattering isotropic target photons for 4 different values of the parameter b: 1, 7, 50, and 100. The energy of gamma-rays is in units of the electron energy. Gray: the gamma-ray spectrum produced by electrons with relativistic Maxwellian distribution; in this case, the photon energies are in units of 4Θ, where Θ is the “temperature” of Maxwellian distribution.