Indirect Detection of Axion Dark Matter with Radio Signals from Neutron Stars

Axions are one of the best-motivated dark matter particle candidates and are able to solve the strong CP problem. In the presence of magnetic fields, axions can resonantly convert to observable photons, making the strong magnetic field within neutron star magnetospheres a natural channel for axion indirect detection. By solving the axion-photon mixing equations and modeling neutron star populations, we calculate the expected radio signal flux due to conversion from several astrophysical targets. Focusing on the Galactic Center of the Milky Way, the globular cluster M54 in the Sagittarius dwarf galaxy, and the Andromeda galaxy, we show that narrow-band radio observations with telescopes such as the Green Bank Telescope and the future Square Kilometer Array will be able to probe the axion parameter space over roughly two orders of magnitude in mass, starting at a fraction of a μeV.