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

We report 21-year 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 short- and long-timescale correlated noise such as jitter and red noise. Its timing residuals have weighted root mean square ∼92 ns. The new data set allows us to update and improve previous measurements of the system properties, including the masses of the neutron star (1.31 ± 0.11 M_⊙) and the companion white dwarf (0.286 ± 0.012 M_⊙) as well as their parallax distance 1.15 ± 0.03 kpc. We measured the intrinsic change in orbital period, {\dot{P}}_{{b}}^{Int}, is -0.20 ± 0.17 ps s^-1, which is not distinguishable from zero. This result, combined with the measured {\dot{P}}_{{b}}^{Int} 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 ± 1.1) × 10^-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}}_{{b}}^{Int} of pulsar binaries can also place limits on the putative coupling constant for dipole gravitational radiation {κ }_{{D}}=(-0.9+/- 3.3)× {10}^-4 (95% confidence). Finally, the nearly circular orbit of this pulsar binary allows us to constrain statistically the strong-field post-Newtonian parameters Δ, which describes the violation of strong equivalence principle, and {\hat{α }}₃, which describes a breaking of both Lorentz invariance in gravitation and conservation of momentum. We found, at 95% confidence, {{Δ }}\lt 0.01 and {\hat{α }}₃\lt 2× {10}^-20 based on PSR J1713+0747.