  We describe multiwavelength optical, X-ray and radio evidences of energetic
mergers in southern galaxy cluster Abell 3376 (A3376, redshift z=0.046, X-ray
luminosity $ \rm L_{X}(0.1-2.4 keV)= 2.48 \times 10^{44} erg s^{-1}$). Here we
report the rare discovery of gigantic, Mpc-scale non-thermal radio structures
(`radio-arcs'), shaped like a pair of bow-shock fronts on the merger axis. We
argue for the shock acceleration origin of the radio emission and discuss the
possibilty of acceleration of very high energy cosmic ray particles in this and
similar clusters. At redshift z=0.04, cluster A3376 is near enough that some of
these primary or secondary cosmic ray components could actually be detected by
new cosmic ray telescopes, particularly the energetic inverse Compton hard
X-ray/gamma-ray photons upto extreme energies $E_{\gamma} \sim 100
{\gamma^{e}_{7}}^{2}$ GeV (where ${\gamma^{e}_{7}}$ is the electron Lorentz
factor in units of $10^7$). Identification of radio or hard X-ray/gamma-ray
emission from structure formation shocks holds a great promise for advancing
current knowledge on shock formation in the IGM. It should provide the first
direct evidence for such shocks, revealing the underlying large-scale
cosmological flows. When combined with hard X-ray or gamma-ray detection, the
radio signal will provide a direct measure of the unknown magnetic fields in
the IGM, thus providing a better understanding of processes leading to IGM
magnetization and also acceleration and propagation of ultra-high energy cosmic
rays.
