2019MNRAS.484.3573C

X-ray observations of bright AGNs in or behind galaxy clusters offer unique capabilities to constrain axion-like particles. Existing analysis technique relies on measurements of the global goodness of fit. We develop a new analysis methodology that improves the statistical sensitivity to ALP-photon oscillations by isolating the characteristic quasi-sinusoidal modulations induced by ALPs. This involves analysing residuals in wavelength space allowing the Fourier structure to be made manifest as well as a machine learning approach. For telescopes with microcalorimeter resolution, simulations suggest these methods give an additional factor of 2 in sensitivity to ALPs compared to previous approaches.