The Impact of Unmodeled Planetary Shapiro Delay on Pulsar Timing Array Sensitivity

In pulsar timing, massive bodies within the solar system cause a Shapiro delay for observed pulses. Although smaller than the delay from the sun, variation from planetary Shapiro delay effects range between 10 and 100 ns for typical pulsars. If the planetary Shapiro delay model is disabled, the effect, dominated by Jupiter, mimics a signal correlating pulse arrival residuals across the sky. For pulsar pairs that have short observation timespans, this correlation signal is dominated by noise corresponding to the proximity to Jupiter at the time of observation. For time spans nearing or exceeding the period of Jupiter’s orbit, the noise is minimized, leaving a near-dipole signal. If not properly modeled, this effect could partially correlate with a gravitational wave signal, making it more difficult to isolate and detect.