Klein-Nishina steps in the energy spectrum of galactic cosmic ray electrons

Understand

The full Klein-Nishina cross section for the inverse Compton scattering interactions of electrons implies a significant reduction of the electron energy loss rate compared to the Thomson limit when the electron energy exceeds the critical Klein-Nishina energy E_K = gamma_K * m_e c^2 = 0.27 m_e^2 c^2/(k_BT), where T denotes the temperature of the photon graybody distribution.

• As a consequence the total radiative energy loss rate of single electrons exhibits sudden drops in the overall energy loss rate ~ gamma ^2 - dependence when the electron energy reaches the critical Klein-Nishina energy.
• The strength of the drop is proportional to the energy density of the photon radiation field.
• The diffuse galactic optical photon fields from stars of spectral type B and G-K lead to critical Klein-Nishina energies of 40 and 161 GeV, respectively.