Rotating gravitational lenses: a kinematic approach
  This paper uses the Kerr geodesic equations for massless particles to derive
an acceleration vector in both Boyer-Lindquist and Cartesian coordinates. As a
special case, the Schwarzschild acceleration due to a non-rotating mass has a
particularly simple and elegant form in Cartesian coordinates. Using forward
integration, these equations are used to plot the caustic pattern due to a
system consisting of a rotating point mass with a smaller non-rotating planet.
Additionally, first and second order approximations to the paths are
identified, which allows for fast approximations of paths, deflection angles
and travel-time delays.
