  In this paper we show that perturbations of the accretion flow within the
central engines of active galctic nuclei (AGN) are likely to form shock waves
in the accreting plasma. Such shocks, which may be either collisional or
collisionless, can contribute to the observed high energy temporal and spectral
variability. Our Rationale is the following: Observations show that the
continuum emission probably originates in an optically thin, hot plasma in the
AGN central engine. The flux and spectrum from this hot plasma varies
significantly over light crossing timescales. several authors have suggested
that macroscopic perturbations contained within this plasma are the sources of
this variability. In order to produce the observed emission the perturbations
must be radiatively coupled with the optically thin hot matter and must also
move with high velocities. We suggest that shocks, which can be very effective
in randomizing the bulk motion of the perturbations, are responsible for this
coupling. Shocks should form in the central engine, because the temperatures
and magnetic fields are probably reduced below their virial values by radiative
dissipation. Perturbations moving at Keplerian speeds, or strong nonlinear
excitations, result in supersonic and super-Alfvenic velocities leading to
shock waves whithin the hot plasma
  We Show that even a perturbation significantly smaller than the emitting
region can form a shock which significantly modifies the continuum emission in
an AGN, and that the spectral and temporal variability from such a shock
generally resemble those of radio quiet AGN. As an example, the shock inducing
perturbation in our model is a small main sequence star, the capturing and
eventual accretion of which are known to be a plausible process. We argue that
