High-energy cosmic rays (relativistic heavy nuclei) play an important
role in heating interstellar matter in the Milky Way(1,2), and they af
fect chemical abundances through collisions with atoms in the interste
llar gas(2). Although it has long been thought that these cosmic rays
arise from supernovae(3,4), direct evidence for such an association ha
s been lacking. Here we report X-ray observations of the remnant of su
pernova 1006, made by the ASCA satellite, which indicate that emission
from the edges of the remnant shell is dominated by radiation from el
ectrons accelerated to energies of similar to 100 TeV within the shock
front. Ions in the shell are likely to have been accelerated to simil
ar energies, thus giving rise to very-high-energy cosmic rays.