Abstract:

The detection and timing of a millisecond pulsar (MSP) in a relativistic orbit around a massive black hole (BH) would allow for an unprecedented probing of the spacetime around the MBH, allowing precision tests of both astrophysics and fundamental physics in the extreme, strong-field regime. The galactic centre or the centres of globular clusters provide prime hunting grounds for these systems.

In this talk I will discuss the observation of radio emission from a tightly-bounded relativistic MSP-BH system. The emission from such a system may suffer severe distortive transfer effects as it propagates towards us, due to both gravitational/relativistic effects and due to the interaction between the emission and the line-of-sight material (cf. the relativistic material near black holes).
When both of these effects are present, we cannot simply sum their effects together or use a simple convolution of the effects assuming that the geodesics (along which the rays are traced) determine in the vacuo condition are still applicable. The trajectory of the ray is now frequency dependent, a consequence of the interaction with the plasma when the ray propagates in a curved spacetime.

Using a covariant ray tracing formulation accounting for the convolution of these gravitational effects with the material interaction, I  investigate the light propagation through cold plasma in a gravitational field due to a spinning black hole and consider the implications for the detection and timing of an extreme mass ratio MPS-BH system.