Constraints on axion-like particle properties with very high energy gamma-ray observations of Galactic sources

TL;DR

This study uses H.E.S.S. observations of Galactic TeV sources to set new constraints on axion-like particles, excluding certain mass ranges and highlighting the potential of future CTA observations to improve these limits.

Contribution

First to constrain ALP masses around a few times 10^{-7} eV using Galactic gamma-ray data, complementing extragalactic source studies.

Findings

H.E.S.S. data excludes ALP masses around a few times 10^{-7} eV.

Upcoming CTA observations can significantly tighten ALP parameter constraints.

Galactic gamma-ray observations are effective in probing ALP properties.

Abstract

Axion-like particles (ALPs) can oscillate to photons and vice versa in electromagnetic fields. The photon-ALP oscillation provides an attractive solution to the apparent transparency of the Universe to TeV photons. The allowed parameter regions for the ALP mass $m_{\rm a}\leq 10^{-7}$ eV have been tightly constrained by the Fermi-LAT and H.E.S.S observations of some extragalactic sources. In this work we show for the first time that the H.E.S.S observations of some TeV sources in the Galactic plane exclude the highest ALP mass region (i.e., $m_{\rm a}\sim {\rm a ~few\times 10^{-7}}$ eV) that accounts for the TeV transparency of the Universe. The upcoming CTA observations of the Galactic TeV sources are shown to be able to improve the constraints significantly.