Dispersion by pulsars, magnetars, fast radio bursts and massive electromagnetism at very low radio frequencies

TL;DR

This paper explores how low-frequency radio observations of pulsars, magnetars, and FRBs can provide new insights into photon mass limits and electromagnetic dispersion, utilizing ground and space-based observatories.

Contribution

It highlights the potential of very low frequency radio astronomy, including new observatories like OLFAR, to test fundamental physics such as photon mass and electromagnetic dispersion effects.

Findings

Dispersion measure excess may indicate photon mass effects.

Low-frequency observatories can improve constraints on photon mass.

Space-based arrays like OLFAR enable observations beyond ionospheric limitations.

Abstract

Our understanding of the universe relies mostly on electromagnetism. As photons are the messengers, fundamental physics is concerned in testing their properties. Photon mass upper limits have been earlier set through pulsar observations, but new investigations are offered by the excess of dispersion measure (DM) sometimes observed with pulsar and magnetar data at low frequencies, or with the fast radio bursts (FRBs), of yet unknown origin. Arguments for the excess of DM do not reach a consensus, but are not mutually exclusive. Thus, we remind that for massive electromagnetism, dispersion goes as the inverse of the frequency squared. Thereby, new avenues are offered also by the recently operating ground observatories in 10-80 MHz domain and by the proposed Orbiting Low Frequency Antennas for Radio astronomy (OLFAR). The latter acts as a large aperture dish by employing a swarm of nano-satellites observing the sky for the first time in the 0.1 - 15 MHz spectrum. The swarm must be deployed sufficiently away from the ionosphere to avoid distortions especially during the solar maxima, terrestrial interference and offer stable conditions for calibration during observations.