We study a mechanism for producing intrinsic broken power-law gamma-ray
spectra in compact sources. This is based on the principles of automatic photon
quenching, according to which, gamma-rays are being absorbed on spontaneously
produced soft photons, whenever the injected luminosity in gamma-rays lies
above a certain critical value. We derive an analytical expression for the
critical gamma-ray compactness in the case of power-law injection. For the case
where automatic photon quenching is relevant, we calculate analytically the
emergent steady-state gamma-ray spectra. We perform also numerical calculations
in order to back up our analytical results. We show that a spontaneously
quenched power-law gamma-ray spectrum obtains a photon index 3{\Gamma}/2, where
{\Gamma} is the photon index of the power-law at injection. Thus, large
spectral breaks of the gamma-ray photon spectrum, e.g. ΔΓ≳1, can be obtained by this mechanism. We also discuss additional features of
this mechanism that can be tested observationally. Finally, we fit the
multiwavelength spectrum of a newly discovered blazar (PKS 0447-439) by using
such parameters, as to explain the break in the gamma-ray spectrum by means of
spontaneous photon quenching, under the assumption that its redshift lies in
the range 0.1<z<0.24.Comment: 14 pages, 9 figures, 2 tables, accepted for publication in A&
