Secular variability, geodetic precession and moment of inertia of binary pulsars

Abstract

More and more binary pulsars show significant secular variations, in which the measured projected semi-major axis, $\dot{x}^{obs}$, and the first derivative of orbital period, $\dot{P}_{b}^{obs}$, are several order of magnitude larger than the prediction of general relativity (GR). This paper shows that the geodetic precession induced orbital effects can explain both $\dot{x}$ and $\dot{P}_{b}$ measured in binary pulsars. Moreover, by this model we can automatically estimate the magnitude of the spin angular momenta of the pulsar and its companion star, and therefore the moment of inertia ($10^{44}$g cm$^2$ to $10^{45}$g cm$^2$) of pulsar of binary pulsar systems, which agrees well with theoretical predictions. In other words, the contamination (residual represented by $\dot{x}$ and $\dot{P}_{b}$) in pulsar timing measurements might be caused by geodetic precession, an interesting gravitational effect we have been seeking for.