Magnetic-Field Amplification in the Thin X-ray Rims of SN1006

TL;DR

This paper investigates the narrow X-ray rims of SN1006, providing evidence for magnetic-field amplification through analysis of rim width energy dependence, and rules out magnetic damping as the primary cause.

Contribution

It extends rim width calculations to include energy-dependent diffusion and applies this to Chandra data, demonstrating magnetic-field amplification in SN1006.

Findings

Rim widths decrease with photon energy, indicating magnetic-field amplification.

Magnetic damping models are inconsistent with observed energy dependence.

Results suggest short mean free paths and energy-dependent diffusion dominate rim formation.

Abstract

Several young supernova remnants (SNRs), including SN1006, emit synchrotron X-rays in narrow filaments, hereafter thin rims, along their periphery. The widths of these rims imply 50 to 100 $\mu$G fields in the region immediately behind the shock, far larger than expected for the interstellar medium compressed by unmodified shocks, assuming electron radiative losses limit rim widths. However, magnetic-field damping could also produce thin rims. Here we review the literature on rim width calculations, summarizing the case for magnetic-field amplification. We extend these calculations to include an arbitrary power-law dependence of the diffusion coefficient on energy, $D \propto E^{\mu}$. Loss-limited rim widths should shrink with increasing photon energy, while magnetic-damping models predict widths almost independent of photon energy. We use these results to analyze Chandra observations of SN 1006, in particular the southwest limb. We parameterize the full widths at half maximum (FWHM) in terms of energy as FWHM $\propto E^{m_E}_{\gamma}$. Filament widths in SN1006 decrease with energy; $m_E \sim -0.3$ to $-0.8$, implying magnetic field amplification by factors of 10 to 50, above the factor of 4 expected in strong unmodified shocks. For SN 1006, the rapid shrinkage rules out magnetic damping models. It also favors short mean free paths (small diffusion coefficients) and strong dependence of $D$ on energy ($\mu \ge 1$).