  Time-dependent injection can cause non-linear cooling effects, which lead to
a faster energy loss of the electrons in jets. The most obvious result is the
appearance of unique breaks in the SED, which would normally be attributed to a
complicated electron distribution. The knowledge of the observation time and
duration is important to interpret the observed spectra, because of the
non-trivial evolution of the SED. Intrinsic gamma-gamma absorption processes in
the emission region are only of minor importance.
