  Massive stars, possibly red supergiants, which retain extended hydrogen
envelopes until core collapse, produce Type II Plateau (IIP) supernovae. The
ejecta from these explosions shock the circumstellar matter originating from
the mass loss of the progenitor during the final phases of its life. This
interaction accelerates particles to relativistic energies which then lose
energy via synchrotron radiation in the shock-amplified magnetic fields and
inverse Compton scattering against optical photons from the supernova. These
processes produce different signatures in the radio and X-ray part of the
electromagnetic spectrum. Observed together, they allow us to break the
degeneracy between shock acceleration and magnetic field amplification. In this
work we use X-rays observations from the Chandra and radio observations from
the ATCA to study the relative importance of processes which accelerate
particles and those which amplify magnetic fields in producing the non-thermal
radiation from SN 2011ja. We use radio observations to constrain the explosion
date. Multiple Chandra observations allow us to probe the history of variable
mass loss from the progenitor. The ejecta expands into a low density bubble
followed by interaction with a higher density wind from a red supergiant
consistent with ZAMS mass greater than 16 solar masses. Our results suggest
that a fraction of type IIP supernovae may interact with circumstellar media
set up by non-steady winds.
