  Variability in active galactic nuclei is observed in ultraviolet to X-ray
emission based light curves. This could be attributed to orbital signatures of
the plasma that constitutes the accretion flow on the putative disk or in the
developing jet close to the inner region of the central black hole. We discuss
some theoretical models which build on this view. These models include general
relativistic effects such as light bending, aberration effects, gravitational
and Doppler redshifts. The novel aspects relate to the treatment of helical
flow in cylindrical and conical geometries in the vicinity of a Schwarzschild
black hole that leads to amplitude and frequency modulations of simulated light
curves as well as the inclusion of beaming effects in these idealized
geometries. We then present a suite of time series analysis techniques
applicable to data with varied properties which can extract detailed
information from them for their use in theoretical models.
