Electron injection by relativistic protons in active galactic nuclei

The authors make the case that efficient acceleration of protons by strong shocks in active galactic nuclei will automatically channel most of the available energy into relativistic electrons and positrons. Thus, direct acceleration of electrons need not be efficient. It is shown that, for the most energetic protons likely to be accelerated in AGNs, p-p collisions are less important than collisions of protons with soft photons. Pairs produced by p-γ collisions in this scenario have much higher energies than the maximum energies attainable by Fermi acceleration of electrons. They are energetic enough to initiate and sustain a pair cascade even when synchrotron radiation is the primary cooling process.