Key Laboratory of Astroparticle Physics of Yunnan Province;
Yunnan University;
Kunming 650091;
China;
Department of Physical Science and Technology;
Kunming University;
Kunming 650214;
China;
Department of Astronomy;
Yunnan University;
Kunming 650091;
China;
gamma rays:ISM; radiation mechanisms:nonthermal; ISM:individual objects:Crab nebula;