Orateur
Description
Axion-Like Particles (ALPs) are well-motivated candidates for light dark matter and may couple with photons in the presence of astrophysical magnetic fields which give rise to the possibility of photon-ALP oscillations. If sufficiently strong, this mixing can induce characteristic energy-dependent feature in gamma-ray spectrum of astrophysical sources.
In this work, we explore the sensitivity of very-high-energy gamma-ray observations to ALP-photon interactions by combining measurements from AGNs located behind galaxy clusters. While the spectral features expected for a single source are highly sensitive to the specific magnetic-field configuration along the line of sight, averaging over a population of AGN-cluster pairs allows statistically robust predictions of the expected signal. To address this, we apply a stacking analysis of multiple AGN-cluster pairs, yielding a controlled prediction of the expected ALP induced spectral patterns and enhancing the sensitivity to such irregularities.
The method is evaluated using simulated observations of hard-spectrum Fermi-LAT AGNs accessible to Cherenkov instruments such as H.E.S.S. The combination of mock H.E.S.S. observations with our stacking approach enable exploration of the previously uncharted ALP dark matter parameter space in the neV mass range.