Constraints on Axion-like Particles from X-Ray Observations of NGC1275

Axion-like particles (ALPs) can induce localized oscillatory modulations in the spectra of photon sources passing through astrophysical magnetic fields. Ultra-deep Chandra observations of the Perseus cluster contain over 5× {10}⁵ counts from the active galactic nucleus (AGN) of the central cluster galaxy NGC1275 and represent a data set of extraordinary quality for ALP searches. We use this data set to search for X-ray spectral irregularities from the AGN. The absence of irregularities at the { O }(30 % ) level allows us to place leading constraints on the ALP-photon mixing parameter {g}_{aγ γ} ≲ 1.4{--}4.0× {10}^-12 {{GeV}}^-1 for {m}_a≲ {10}^-12 {eV}, depending on assumptions on the magnetic field realization along the line of sight.