TESTING THEORIES OF GRAVITATION USING 21-YEAR TIMING OF PULSAR BINARY J1713+0747

Abstract

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