X-ray Stripes in Tycho's Supernova Remant: Synchrotron Footprints of a Nonlinear Cosmic Ray-driven Instability

TL;DR

This paper explains the X-ray stripes observed in Tycho's supernova remnant as a result of nonlinear cosmic-ray driven magnetic turbulence, linking shock physics, magnetic field amplification, and particle acceleration.

Contribution

The study presents a nonlinear diffusive shock acceleration model that predicts stripe patterns and polarization consistent with observations, advancing understanding of magnetic turbulence in supernova remnants.

Findings

Stripes are caused by cosmic-ray generated magnetic turbulence.

Maximum CR proton energy estimated at ~10^15 eV.

Predicted X-ray polarization pattern with ~50% polarization fraction.

Abstract

High-resolution Chandra observations of Tycho's 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 requires the simultaneous action of a number of shock-plasma phenomena and 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 cosmic-ray current driven instability, does predict stripes consistent with the synchrotron emission 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 $\sim 10^{15}$\,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.