Supernova enhanced cosmic ray ionization and induced chemistry in a
  molecular cloud of W51C
  Cosmic rays pervade the Galaxy and are thought to be accelerated in supernova
shocks. The interaction of cosmic rays with dense interstellar matter has two
important effects: 1) high energy (>1 GeV) protons produce {\gamma}-rays by
{\pi}0-meson decay; 2) low energy (< 1 GeV) cosmic rays (protons and electrons)
ionize the gas. We present here new observations towards a molecular cloud
close to the W51C supernova remnant and associated with a recently discovered
TeV {\gamma}-ray source. Our observations show that the cloud ionization degree
is highly enhanced, implying a cosmic ray ionization rate ~ 10-15 s-1, i.e. 100
times larger than the standard value in molecular clouds. This is consistent
with the idea that the cloud is irradiated by an enhanced flux of freshly
accelerated low-energy cosmic rays. In addition, the observed high cosmic ray
ionization rate leads to an instability in the chemistry of the cloud, which
keeps the electron fraction high, ~ 10-5, in a large fraction (Av \geq 6mag) of
the cloud and low, ~ 10-7, in the interior. The two states have been predicted
in the literature as high- and low-ionization phases (HIP and LIP). This is the
observational evidence of their simultaneous presence in a cloud.
