X-ray stripes in Tycho's supernova remnant: Synchrotron footprints of a nonlinear cosmic-ray-driven instability

High-resolution Chandra observations of Tycho's supernova remnant (SNR) have revealed several sets of quasi-steady, high-emissivity, nearly parallel X-ray stripes in some localized regions of the SNR. These stripes are most likely the result of cosmic-ray (CR) generated magnetic turbulence at the SNR blast wave. However, for the amazingly regular pattern of these stripes to appear, simultaneous action of a number of shock-plasma phenomena is required, which is not predicted by most models of magnetic field amplification. A consistent explanation of these stripes yields information on the complex nonlinear plasma processes connecting efficient CR acceleration and magnetic field fluctuations in strong collisionless shocks. The nonlinear diffusive shock acceleration (NL-DSA) model described here, which includes magnetic field amplification from a CR-current-driven instability, does predict stripes consistent with the synchrotron observations of Tycho's SNR. We argue that the local ambient mean magnetic field geometry determines the orientation of the stripes and therefore it can be reconstructed with the high-resolution X-ray imaging. The estimated maximum energy of the CR protons responsible for the stripes is ∼10¹⁵ eV. Furthermore, the model predicts that a specific X-ray polarization pattern, with a polarized fraction ∼50%, accompanies the stripes, which can be tested with future X-ray polarimeter missions.