Searching for axion dark matter with the MeerKAT radio telescope
Yun-Fan Zhou, Nick Houston, G. I. G. Józsa, Hao Chen, Yin-Zhe Ma, Qiang Yuan, Tao An, Yogesh Chandola, Ran Ding, Fujun Du, Shaoguang Guo, Xiaoyuan Huang, Mengtian Li, Chandreyee Sengupta
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 centerd at the frequency of the axion mass. We point the MeerKAT radio telescope towards the isolated neutron star $\mathrm{J}0806.4\ensuremath{-}4123$ 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 $5\ensuremath{\sigma}$ in the data, we provide a unique constraint on the Primakoff coupling of axion DM, ${g}_{\mathrm{a}\ensuremath{\gamma}\ensuremath{\gamma}}\ensuremath{\lesssim}9.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$ at the 95% confidence level, in the mass range $3.18--4.35\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. This result serves the strongest constraint in the axion mass range $4.20--4.35\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$.