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 > 10M , 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. Subject headings: pulsars: binaries, relativity Binary pulsars are excellent laboratories for testing General Relativity (GR) and other theories of gravity. Long-term timing observations of relativistic binaries, such as PSR B1913+16 (Hulse & Taylor 1975), yield highly precise measurements of post-Keplerian orbital parameters of the pulsar. In particular, observations of the the orbital decay of PSR B1913+16 induced by gravitational radiative effects have verified the validity of GR to within 0.5% (Taylor & Weisberg 1989). Recently, pulsar surveys have unveiled additional relativistic binary pulsars (for a recent review see Wolszczan (1997)). Of particular interest is PSR B1534+12 (Wolszczan 1991, Taylor et al., 1992), in which case the presence of post–Keplerian orbital effects and proximity of the pulsar to Earth give this object a potential to become an exceptionally precise probe of relativistic gravity. [email protected] [email protected]