Relativistic imprints on dispersion measure space distortions

Abstract

We investigate the three-dimensional clustering of sources emitting electromagnetic pulses traveling through cold electron plasma, whose radial distance is inferred from their dispersion measure. As a distance indicator, dispersion measure is systematically affected by inhomogeneities in the electron density along the line of sight and special and general relativistic effects, similar to the case of redshift surveys. We present analytic expressions for the correlation function of fast radio bursts (FRBs), and for the galaxy-FRB cross-correlation function, in the presence of these dispersion measure-space distortions. We find that the even multipoles of these correlations are primarily dominated by non-local contributions (e.g. the electron density fluctuations integrated along the line of sight), while the dipole also receives a significant contribution from the Doppler effect, one of the major relativistic effects. A large number of FRBs, $\mathcal{O}(10^{5}\sim10^{6})$, expected to be observed in the Square Kilometre Array, would be enough to measure the even multipoles at very high significance, ${\rm S}/{\rm N} \approx 100$, and perhaps to make a first detection of the dipole (${\rm S}/{\rm N} \approx 10$) in the FRB correlation function and FRB-galaxy cross correlation function. This measurement could open a new window to study and test cosmological models.