The injection problem is one of the biggest but unresolved issue to understand the origin of
Galactic cosmic rays. To evaluate the injection energy quantitatively, we need to measure how
much energy is stolen from the background thermal plasma. The injection of energy to energetic
particles causes colder plasma than expected from the Rankine-Hugoniot relation in the ideal gas
cases.
We measure the electron temperature gradient in the northwestern, post-shock region of SN 1006
with Chandra. It is found that the electron temperature increases from 0.52–0.62 keV at the
outer edge to 0.82−0.95 keV at the inner region, 0.6 pc away from the shock front. This
temperature change is lower than that expected from the Coulomb scattering, implying significant
energy injection into particle acceleration in this region. For a more detailed understanding, we
need observations with higher energy resolutions that will be available with XRISM and Athena.