English: The sun as seen in gamma rays by COMPTEL during a June 15, 1991, solar flare. The sun is ordinarily not known to produce gamma rays, but during this solar flare, steams of neutrons poured into the intrastellar medium to create gamma rays. This image provided the first evidence that the sun can accelerate particles for several hours. This phenomenon was not observed before CGRO and represents a new understanding of solar flares. COMPTEL data is analyzed jointly by the Max Planck Institute for Extraterrestrial Physics, which also helped build the instrument; NASA's Goddard Space Flight Center, which operates CGRO; Science Department of the Astrophysics Division of ESA/ESTEC in Noordwijk, Netherlands; and the University of New Hampshire.