It is shown that the nonlinear kinetic theory of cosmic ray ( CR ) acceleration in supernova remnants ( SNRs ) describes the shell-type nonthermal X-ray morphology of Cas A , obtained in Chandra observations , in a satisfactory way .
The set of empirical parameters , like distance , source size and total energy release , is the same which reproduces the dynamical properties of the SNR and the spectral characteristics of the emission produced by CRs .
The extremely small spatial scales in the observed morphological structures at hard X-ray energies are due to a large effective magnetic field B _ { \mathrm { d } } \sim 500 \mu G in the interior which is at the same time not only required but also sufficient to achieve the excellent agreement between the spatially integrated radio and X-ray synchrotron spectra and their calculated form .
The only reasonably thinkable condition for the production of such a large effective field strength is a very efficiently accelerated nuclear CR component .
Therefore the Chandra data confirm first of all the inference that Cas A indeed accelerates nuclear CRs with the high efficiency required for Cas A to be considered as a member of the main class of Galactic CR sources and , secondly , that the nonlinear kinetic theory of CR acceleration in SNRs is a reliable method to determine the magnetic field value in SNRs .