Axion search with telescope for radio astronomy (ASTRA): forecast for observations between 0.5 and 4~GHz

TL;DR

This paper evaluates the potential of a 5-meter radio telescope to detect axion-like particles through their conversion into radio waves near neutron stars, covering 0.5 to 4 GHz, and discusses strategies for expanding the search across broader frequency ranges.

Contribution

It provides a detailed forecast for axion detection using a new radio telescope, including models, strategies, and the potential to explore previously inaccessible parameter space.

Findings

Detects axion-like particles in the 2-17 μeV mass range.

Can improve existing neutron star observations by over an order of magnitude.

Sensitive to QCD axion models if a DM spike exists at the Galactic center.

Abstract

Axion dark matter (DM) is predicted to convert into radio waves in neutron star magnetospheres. We assess the detectability of this signal using a 5 m radio telescope to be installed at the Fan Mountain Observatory, operating in the UHF, L- and S-bands from 0.5 to 4~GHz. We demonstrate that such a telescope can search new parameter space for axion-like particles over a broad range from $2\,\mu\text{eV}<m_a<17\,\mu\text{eV}$ for axion-photon couplings $g_{a\gamma\gamma} \gtrsim 2\times 10^{-12}\text{ GeV}^{-1}$ with a three year observing period assuming the standard halo model -- improving neutron star observations by more than an order of magnitude. The search is broadband and is thus complementary to other techniques in the same frequency range. We describe in detail our neutron star population model, noise model, and proposed observing strategy. Most constraining power comes from neutron stars at the Galactic centre, where the smooth DM halo is densest. If a DM spike exists at the Galactic centre, the search is sensitive in the QCD axion model band. UHF and L-band observations (0.5 to 2~GHz) represent the pathfinder phase of a wider program we call ``Axion Search with Telescope for Radio Astronomy'' (ASTRA). Future higher mass searches aimed at discovery potential for the post-inflation axion require further hardware development to cover S, C, X and Ku bands (2 to 18~GHz).