Time delay in binary systems

The aim of this paper is to study the time delay on electromagnetic signals propagating across a binary stellar system. We focus on the antisymmetric gravitomagnetic contribution due to the angular momentum of one of the stars of the pair. Considering a pulsar as the source of the signals, the effect would be manifest both in the arrival times of the pulses and in the frequency shift of their Fourier spectra. We derive the appropriate formulas and we discuss the influence of different configurations on the observability of gravitomagnetic effects. We argue that the recently discovered PSR J0737-3039 binary system does not permit the detection of the effects because of the large size of the eclipsed region.

Figure 1

Gravitomagnetic reference frame $xyz$. The origin is located on ${\mathcal{O}}_2$ and the $z$ axis is aligned with the direction of its angular momentum. The Cartesian reference frame $XYZ$ is located in ${\mathcal{O}}_2$ and $XY$ identifies the orbital plane of the binary system.

Figure 2

The function $\tau (\phi )$ (measured in picoseconds) versus the orbital phase of star A in proximity to the occultation position $\phi =\pi$. The horizontal dashed line corresponds to the detectability threshold of ${10}^{-8}\mathrm{s}$.