Searching for axion dark matter with the MeerKAT radio telescope

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 centerd 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 modeling the conversion process of infalling axion dark matter (DM), we then compare these spectra to theoretical expectations for a given choice of axion parameters. Whilest finding no signal above 5 sigma in the data, we provide a unique constraint on the Primakoff coupling of axion DM, ga gamma gamma less than or similar to 9.3 x 10-12 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.