Trans-Alfvénic magnetohydrodynamic turbulence in the vicinity of supernova remnant Cassiopeia-A shocks

Abstract

ABSTRACT Statistics of the magnetic field disturbances in supernova remnants (SNRs) can be accessed using the second-order correlation function of the synchrotron intensities. Here we measure the magnetic energy spectra in the 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 a 2/3 power law over the decade of range scales, showing the developed trans-Alfvénic magnetohydrodynamic turbulence. Our results are globally consistent with the theoretical prediction of trans-Alfvénic Mach number in developed magnetohydrodynamic turbulence and can be explained by amplification of the magnetic field in the vicinity of SNR shocks. The magnetic energy spectra predict SNR Cassiopeia-A to have an additional subshock in the radio frequency observation along with forward and reverse shocks, with a radial window of the amplified magnetic field of ∼ 0.115 pc near the shocks.