A Realistic Pulsar–Supermassive Black Hole Timing Model

Timing observations of pulsars orbiting around a supermassive black hole (SMBH) can measure the spacetime around the SMBH to a high precision and thus be a novel probe of the gravity theory. Future high-frequency surveys of the Galactic center (GC) region to be performed by the next-generation radio telescopes, such as the Square Kilometre Array, may discover pulsars that orbit around Sagittarius A* (Sgr A*), the SMBH dwelling in our GC. In this paper, we present a realistic pulsar–SMBH timing model based on the post-Newtonian equations of motion of the pulsar. Considering the timing precision expected in the future, we take into account several next-to-leading-order light propagation time delays in the timing model. For the first time, we include the effects of proper motion of Sgr A*, which were expected to break the spin measurement degeneracy. We forecast the measurement precision of various parameters of Sgr A*, and discuss the data analysis procedure in the presence of red noise, which can be strong if the pulsar is a normal pulsar. The realistic timing model constructed in this study will serve as a useful tool in future searching and timing of pulsar–SMBH systems in the GC.