  Aims: We investigate photon quenching in compact non-thermal sources. This
involves photon-photon annihilation and lepton synchrotron radiation in a
network that can become non-linear. As a result the gamma-ray luminosity of a
source cannot exceed a critical limit that depends only on the radius of the
source and on the magnetic field. Methods: We perform analytic and numerical
calculations that verify previous results and extend them so that the basic
properties of photon quenching are investigated. Results: We apply the above to
the 2006 TeV observations of quasar 3C279 and obtain the parameter space of
allowed values for the radius of the emitting source, its magnetic field
strength and the Doppler factor of the flow. We argue that the TeV observations
favour either a modest Doppler factor and a low magnetic field or a high
Doppler factor and a high magnetic field.
