It has been suggested that high-energy gamma-ray emission (>100MeV)
of nearby star-forming galaxies may be produced predominantly by cosmic rays
colliding with the interstellar medium through neutral pion decay. The
pion-decay mechanism predicts a unique spectral signature in the gamma-ray
spectrum, characterized by a fast rising spectrum and a spectral break below a
few hundreds of MeV. We here report the evidence of a spectral break around 500
MeV in the disk emission of Large Magellanic Cloud (LMC), which is found in the
analysis of the gamma-ray data extending down to 60 MeV observed by {\it
Fermi}-Large Area Telescope. The break is well consistent with the pion-decay
model for the gamma-ray emission, although leptonic models, such as the
electron bremsstrahlung emission, cannot be ruled out completely.Comment: 11 pages, 4 figures, Accepted by Ap
