  The recently launched satellite, Fermi Gamma-ray Space Telescope, is expected
to find out if cosmic-ray (CR) protons are generated from supernova remnants
(SNRs), especially RX J1713.7-3946, by observing the GeV-to-TeV gamma-rays. The
GeV emission is thought to be bright if the TeV emission is hadronic, i.e., of
proton origin, while dim if leptonic. We reexamine the above view using a
simple theoretical model of nonlinear acceleration of particles to calculate
the gamma-ray spectrum of Galactic young SNRs. If the nonlinear effects of CR
acceleration are considered, it may be impossible to distinguish the evidence
of proton acceleration from leptonic in the gamma-ray spectrum of Galactic
young SNRs like RX J1713.7-3946. On the other hand, future km^3-class neutrino
observations will likely find a clear evidence of the proton acceleration
there.
