Constraints on Axion-Like Particles from Non-Observation of Spectral Modulations for X-ray Point Sources

We extend previous searches for X-ray spectral modulations induced by ALP-photon conversion to a variety of new sources, all consisting of quasars or AGNs located in or behind galaxy clusters. We consider a total of seven new sources, with data drawn from the Chandra archive. In all cases the spectrum is well fit by an absorbed power-law with no evidence for spectral modulations, allowing constraints to be placed on the ALP-photon coupling parameter $g_{a\gamma\gamma}$. Two sources are particularly good: the Seyfert galaxy 2E3140 in A1795 and the AGN NGC3862 within the cluster A1367, leading to 95\% bounds for light ALPs ($m_a \lesssim 10^{-12} {\rm eV}$) of $g_{a\gamma\gamma} \lesssim 1.5 \times 10^{-12} {\rm GeV}^{-1}$ and $g_{a\gamma\gamma} \lesssim 2.4 \times 10^{-12} {\rm GeV}^{-1}$ respectively.