Trans-Alfvenic Magnetohydrodynamic Turbulence in the Vicinity of
  Supernova Remnant Cassiopeia-A Shocks
  Statistics of the magnetic field disturbances in the supernova remnants
(SNRs) can be accessed using the second-order correlation function of the
synchrotron intensities. Here we measure the magnetic energy spectra in
supernova remnant Cassiopeia-A by two-point correlation of the synchrotron
intensities, using a recently developed unbiased method. The measured magnetic
energy spectra in the vicinity of supernova remnant shocks are found to be 2/3
power law over the decade of range scales, showing the developed trans-Alfvenic
magnetohydrodynamic turbulence. Our results are globally consistent with the
theoretical prediction of trans-Alfvenic Mach number in developed
magneto-hydrodynamic turbulence and can be explained by the amplification of
the magnetic field in the vicinity of SNR shocks. The magnetic energy spectra
predict SNR Cassiopeia-A having an additional subshock in the radio frequency
observation along with forward and reverse shocks, with a radial window of the
amplified magnetic field of ~ 0.115pc near the shocks
