Testing Theories of Gravitation Using 21-Year Timing of Pulsar Binary J1713+0747

TL;DR

This 21-year pulsar timing study tests gravitational theories by measuring orbital parameters and constraining variations in the gravitational constant, providing the most stringent limits from pulsar binaries to date.

Contribution

The paper presents the longest timing dataset for PSR J1713+0747, improving measurements of system properties and setting new limits on gravitational constant variation and alternative gravity theories.

Findings

Measured orbital period change consistent with zero

Set the tightest limit on G/G from pulsar binaries

Constrained strong-field post-Newtonian parameters  and _3

Abstract

We report 21-yr timing of one of the most precise pulsars: PSR J1713+0747. Its pulse times of arrival are well modeled by a comprehensive pulsar binary model including its three-dimensional orbit and a noise model that incorporates correlated noise such as jitter and red noise. Its timing residuals have weighted root mean square $\sim 92$ ns. The new dataset allows us to update and improve previous measurements of the system properties, including the masses of the neutron star ($1.31\pm0.11$ $M_{\odot}$) and the companion white dwarf ($0.286\pm0.012$ $M_{\odot}$) and the parallax distance $1.15\pm0.03$ kpc. We measured the intrinsic change in orbital period, $\dot{P}^{\rm Int}_{\rm b}$, is $-0.20\pm0.17$ ps s$^{-1}$, which is not distinguishable from zero. This result, combined with the measured $\dot{P}^{\rm Int}_{\rm b}$ of other pulsars, can place a generic limit on potential changes in the gravitational constant $G$. We found that $\dot{G}/G$ is consistent with zero [$(-0.6\pm1.1)\times10^{-12}$ yr$^{-1}$, 95\% confidence] and changes at least a factor of $31$ (99.7\% confidence) more slowly than the average expansion rate of the Universe. This is the best $\dot{G}/G$ limit from pulsar binary systems. The $\dot{P}^{\rm Int}_{\rm b}$ of pulsar binaries can also place limits on the putative coupling constant for dipole gravitational radiation $\kappa_D=(-0.9\pm3.3)\times10^{-4}$ (95\% confidence). Finally, the nearly circular orbit of this pulsar binary allows us to constrain statistically the strong-field post-Newtonian parameters $\Delta$, which describes the violation of strong equivalence principle, and $\hat{\alpha}_3$, which describes a breaking of both Lorentz invariance in gravitation and conservation of momentum. We found, at 95\% confidence, $\Delta<0.01$ and $\hat{\alpha}_3<2\times10^{-20}$ based on PSR J1713+0747.