We discuss our recent constraints on the coupling of Very-Light Axion-Like
Particles (of masses <10β12Β eV) to electromagnetism from
Chandra observations of the cluster-hosted Active Galactic Nuclei (AGN)
H1821+643 and NGC1275. In both cases, the inferred high-quality AGN spectra
excluded all photon-ALP couplings gaΞ³β>(6.3β8.0)Γ10β13Β GeVβ1 at the 99.7% level, respectively, based on
the non-detection of spectral distortions attributed to photon-ALP
inter-conversion along the cluster line-of-sight. Finally, we present the
prospects of tightening current bounds on such ALPs by up to a factor of 10
with next-generation X-ray observatories such as Athena, AXIS and LEM
given their improved spectral and spatial resolution and collecting area
compared to current missions.Comment: 4 pages, 1 figure. Accepted for publication to Memorie della SAIt for
the Proceedings of the European Astronomical Society 2022 (EAS 2022) Annual
Meeting Symposium S3 "The Dark matter multi-messenger challenge