The post-Newtonian mean anomaly advance as further post-Keplerian parameter in pulsar binary systems

TL;DR

This paper derives the post-Newtonian mean anomaly rate in pulsar binaries within General Relativity, proposing it as a new post-Keplerian parameter that can improve tests of gravitational theories.

Contribution

It introduces the mean anomaly advance as a new post-Keplerian parameter, larger than periastron advance, useful for constraining gravity theories in pulsar systems.

Findings

The mean anomaly advance can be nearly three times larger than periastron advance.

It can be extracted from orbital phase data with high precision.

Applicable to pulsar-white dwarf systems with limited post-Keplerian measurements.

Abstract

The post-Newtonian gravitoelectric secular rate of the mean anomaly M is worked out for a two-body system in the framework of the General Theory of Relativity. The possibility of using such an effect, which is different from the well known decrease of the orbital period due to gravitational wave emission, as a further post-Keplerian parameter in binary systems including one pulsar is examined. The resulting effect is almost three times larger than the periastron advance \dot\omega. E.g., for the recently discovered double pulsar system PSR J0737-3039 A+B it would amount to -47.79 deg yr^-1. This implies that it could be extracted from the linear part of a quadratic fit of the orbital phase because the uncertainties both in the linear drift due to the mean motion and in the quadratic shift due to the gravitational wave are smaller. The availability of such additional post-Keplerian parameter would be helpful in further constraining the General Theory of Relativity, especially for such systems in which some of the other post-Keplerian parameters can be measured with limited accuracy. Moreover, also certain pulsar-white dwarf binary systems, characterized by circular orbits like PSR B1855+09 and a limited number of measured post-Keplerian parameters, could be used for constraining competing theories of gravity.