Pulse arrival times from binary pulsars with rotating black hole companions

We present a study of the gravitational time delay of arrival of signals from binary pulsar systems with rotating black hole companions. In particular, we investigate the strength of this effect (Shapiro delay) as a function of the inclination, eccentricity, and period of the orbit, as well as the mass and angular momentum of the black hole. This study is based on direct numerical integration of null geodesics in a Kerr background geometry. We find that, for binaries with sufficiently high orbital inclinations (>89°) and compact companion masses greater than 10 M_⊙, the effect arising from the rotation of the black hole in the system amounts to a microsecond-level variation of the arrival times of the pulsar pulses. If measurable, this variation could provide a unique signature for the presence of a rotating black hole in a binary pulsar system.