Automatic quenching of high energy γ-ray sources by synchrotron photons

We investigate a magnetized plasma in which injected high energy gammarays annihilate on a soft photon field, that is provided by the synchrotron radiation of the created pairs. For a very wide range of magnetic fields, this process involves gamma-rays between 0.3GeV and 30TeV. We derive a simple dynamical system for this process, analyze its stability to runaway production of soft photons and paris, and find conditions for it to automatically quench by reaching a steady state with an optical depth to photon-photon annihilation larger than unity. We discuss applications to broad-band γ-ray emitters, in particular supermassive black holes. Automatic quenching limits the gamma-ray luminosity of these objects and predicts substantial pair loading of the jets of less active sources. Subject headings: radiation mechanisms: non-thermal — gamma-rays: theory — galaxies: active