  Multiwavelength observations of high energy flare in 1996 from 3C 279 seems
to favour the so called mirror model between different inverse Compton
scattering models proposed as a possible explanation of gamma-ray emission in
blazars. We performed kinematic analysis of the relativistic blob - mirror
system and found that only part of the mirror located very close to the jet
axis (very likely inside the jet cone) can re-emit soft photons which serve as
a target for production of $\gamma$-rays by relativistic electrons in the blob.
Since the presence of well localized scattering mirror inside the jet is
problematic, this makes problems for the mirror model. The time scale and the
shape of the $\gamma$-ray flare should reflect, in terms of the mirror model,
the blob dimensions and the longitudinal distribution of relativistic electrons
inside the blob. For the $\gamma$-ray light curve of the type observed in 1996
from 3C 279, i.e. the rising time of the flare during a few days with a sharp
cut-off towards the end of the flare, the density of electrons inside the blob
should increase exponentially starting from the front of the blob and reach
maximum towards the end of the blob. Such distribution of electrons is
difficult to explain in a model of a relativistic shock moving along the jet,
which would rather inject electrons more efficiently at the front of the blob
with a trail of particles on its downstream side.
