  We investigate the propagation of light through a plasma on a background Kerr
spacetime via a Hamiltonian formulation. The behaviour of light when
propagating through a vacuum and through a plasma is not the same; the
convolution of gravitational and plasma effects gives rise to a dispersion in
both space and time. The magnitude of the dispersion is a strong function of
both the ray frequency and impact parameter. We discuss implications for the
detection of gravitationally bent pulsar beams near the Galactic centre.
