Searching for axion dark matter with MeerKAT Radio Telescope

TL;DR

This study used the MeerKAT radio telescope to search for axion dark matter signals from a neutron star, setting new constraints on axion-photon coupling in a specific mass range.

Contribution

First observational search for axion dark matter converting into photons near a neutron star using MeerKAT, providing the strongest constraints in a specific mass window.

Findings

No signal detected above 5σ significance.

Set upper limit on axion-photon coupling at 95% confidence.

Constrained axion mass range 3.18-4.35 μeV.

Abstract

Axions provide a natural and well-motivated dark matter candidate, with the capability to convert directly to photons in the presence of an electromagnetic field. A particularly compelling observational target is the conversion of dark matter axions into photons in the magnetospheres of highly magnetised neutron stars, which is expected to produce a narrow spectral peak centred at the frequency of the axion mass. We point the MeerKAT radio telescope towards the isolated neutron star J0806.4$-$4123 for $10$-hours of observation and obtain the radio spectra in the frequency range $769$-$1051$ MHz. By modelling the conversion process of infalling axion dark matter (DM), we then compare these spectra to theoretical expectations for a given choice of axion parameters. Whilst finding no signal above $5\sigma$ in the data, we provide a unique constraint on the Primakoff coupling of axion DM, $g_{{\rm a}\gamma\gamma}\lesssim 9.3 \times 10^{-12}\,{\rm GeV}^{-1}$ at the $95\%$ confidence level, in the mass range $3.18$-$4.35\,\mu$eV. This result serves the strongest constraint in the axion mass range $4.20$-$4.35\,\mu$eV.