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

Understand

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.