section_path: External impact/Cosmic rays
section_name: Cosmic rays
paragraph_text: Cosmic rays
  
  Supernova remnants are thought to accelerate a large fraction of galactic primary cosmic rays, but direct evidence for cosmic ray production has only been found in a small number of remnants. Gamma rays from pion -decay have been detected from the supernova remnants IC 443 and W44. These are produced when accelerated protons from the remnant impact on interstellar material.