Radio timing in a millisecond pulsar-extreme/intermediate mass ratio binary system

TL;DR

This paper compares post-Keplerian and fully relativistic models for pulsar timing near black holes, highlighting the importance of higher order effects for accurate system parameter estimation in extreme gravitational environments.

Contribution

It demonstrates the significance of higher order relativistic effects in pulsar timing models near black holes, improving accuracy over traditional post-Keplerian approximations.

Findings

Significant discrepancies between post-Keplerian and relativistic timing delays.

Higher order relativistic effects are crucial for precise pulsar timing.

Correct modeling impacts detection and parameter estimation of pulsars near black holes.

Abstract

Radio timing observations of a millisecond pulsar in orbit around the Galactic centre black hole (BH) or a BH at the centre of globular clusters could answer foundational questions in astrophysics and fundamental physics. Pulsar radio astronomy typically employs the post-Keplerian approximation to determine the system parameters. However, in the strong gravitational field around the central BH, higher order relativistic effects may become important. We compare the pulsar timing delays given by the post-Keplerian approximation with those given by a relativistic timing model. We find significant discrepancies between the solutions derived for the Einstein delay and the propagation delay (i.e. Roemer and Sharpiro delay) compared to the fully relativistic solutions. Correcting for these higher order relativistic effects is essential in order to construct accurate radio timing models for pulsar systems at the Galactic centre and the centre of globular clusters and informing issues related to their detection.