Leading Axion-Photon Sensitivity with NuSTAR Observations of M82 and M87

TL;DR

This study uses NuSTAR X-ray data from M82 and M87 to set the most sensitive limits yet on ultralight axion-photon coupling, finding no evidence for axions in the targeted energy range.

Contribution

It introduces a novel method combining stellar population analysis and magnetic field modeling to constrain axion properties using X-ray observations.

Findings

No evidence for axions in the data.

Established upper limits on axion-photon coupling.

Improved constraints compared to previous searches.

Abstract

We perform the most sensitive search to-date for the existence of ultralight axions using data from the NuSTAR telescope. We search for stellar axion production in the M82 starburst galaxy and the M87 central galaxy of the Virgo cluster and then the subsequent conversion into hard X-rays in the surrounding magnetic fields. We sum over the full stellar populations in these galaxies when computing the axion luminosity, and we account for the conversion of axions to photons by using magnetic field profiles in simulated IllustrisTNG analogue galaxies. We show that analyzing NuSTAR data towards these targets between roughly 30 to 70 keV shows no evidence for axions and leads to robust constraints on the axion-photon coupling at the level of $|g_{a\gamma\gamma}| \lesssim 6.4 \times 10^{-13}$ GeV$^{-1}$ for $m_a \lesssim 10^{-10}$ eV at 95% confidence.