Fresnel Models for Gravitational Wave Effects on Pulsar Timing

TL;DR

This paper introduces a Fresnel formalism for modeling gravitational wave effects on pulsar timing, enabling new measurements like source distance and chirp mass, and discusses observational requirements for future pulsar timing arrays.

Contribution

It develops a more general Fresnel formalism for gravitational wave effects in pulsar timing, extending beyond the traditional plane-wave approximation.

Findings

Fresnel corrections enable direct measurement of source distance and chirp mass.

Future pulsar timing arrays need sub-100 ns precision and distant pulsars for effective probing.

Source localization can be improved to sub-arcminute accuracy with these methods.

Abstract

Merging supermassive black hole binaries produce low-frequency gravitational waves, which pulsar timing experiments are searching for. Much of the current theory is developed within the plane-wave formalism, and here we develop the more general Fresnel formalism. We show that Fresnel corrections to gravitational wave timing residual models allow novel measurements to be made, such as direct measurements of the source distance from the timing residual phase and frequency, as well as direct measurements of chirp mass from a monochromatic source. Probing the Fresnel corrections in these models will require future pulsar timing arrays with more distant pulsars across our Galaxy (ideally at the distance of the Magellanic Clouds), timed with precisions less than $100$ ns, with distance uncertainties reduced to the order of the gravitational wavelength. We find that sources with chirp mass of order $10^9 \ \mathrm{M}_\odot$ and orbital frequency $\omega_0 > 10$ nHz are good candidates for probing Fresnel corrections. With these conditions met, the measured source distance uncertainty can be made less than 10 per cent of the distance to the source for sources out to $\sim 100$ Mpc, source sky localization can be reduced to sub-arcminute precision, and source volume localization can be made to less than $1 \ \text{Mpc}^3$ for sources out to 1-Gpc distances.