  Understanding the origin of the highest energy cosmic rays is a crucial step
in probing new physics at energies unattainable by terrestrial accelerators.
Their sources remain an enigma half a century after their discovery. They must
be accelerated in the local universe as otherwise interaction with cosmic
background radiations would severely deplete the flux of protons and nuclei at
energies above the Greisen-Zatsepin-Kuzmin (GZK) limit. Hypernovae, nearby
GRBs, AGNs and their flares have all been suggested and debated in the
literature as possible sources. Type Ibc supernovae have a local sub-population
with mildly relativistic ejecta which are known to be sub-energetic GRBs or
X-Ray Flashes for sometime and more recently as those with radio afterglows but
without detected GRB counterparts, such as SN 2009bb. In this work we measure
the size-magnetic field evolution, baryon loading and energetics of SN 2009bb
using its radio spectra obtained with VLA and GMRT. We show that the
engine-driven SNe lie above the Hillas line and they can explain the
characteristics of post-GZK UHECRs.
