  Supernovae provide a backdrop from which we can probe the end state of
stellar evolution in the final years before the progenitor star explodes. As
the shock from the supernova expands, the timespan of mass loss history we are
able to probe also extends, providing insight to rapid time-scale processes
that govern the end state of massive stars. While supernovae transition into
remnants on timescales of decades to centuries, observations of this phase are
currently limited. Here we present observations of SN 1970G, serendipitously
observed during the monitoring campaign of SN 2011fe that shares the same host
galaxy. Utilizing the new Jansky Very Large Array upgrade and a deep X-ray
exposure taken by the Chandra Space Telescope, we are able to recover this
middle-aged supernova and distinctly resolve it from the HII cloud with which
it is associated. We find that the flux density of SN 1970G has changed
significantly since it was last observed - the X-ray luminosity has increased
by a factor of ~3, while we observe a significantly lower radio flux of only
27.5 micro-Jy at 6.75 GHz, a level only detectable through the upgrades now in
operation at the Jansky Very Large Array. These changes suggest that SN 1970G
has entered a new stage of evolution towards a supernova remnant, and we may be
detecting the turn-on of the pulsar wind nebula. Deep radio observations of
additional middle-aged supernovae with the improved radio facilities will
provide a statistical census of the delicate transition period between
supernova and remnant.
