Energy Dependence of Synchrotron X-Ray Rims in Tycho's Supernova Remnant

TL;DR

This study investigates the origin of thin X-ray rims in Tycho's supernova remnant, analyzing their energy dependence and magnetic field structure to distinguish between loss-limited and damping models, ultimately favoring magnetic damping with amplified fields.

Contribution

The paper provides a comprehensive analysis combining X-ray and radio data to favor magnetic damping over simple amplification as the cause of thin rims in Tycho's SNR.

Findings

Rim widths decrease with increasing energy.

Magnetic damping lengths are about 1-5% of the remnant radius.

Magnetic fields are amplified to 50-400 μG, exceeding simple shock compression.

Abstract

Several young supernova remnants exhibit thin X-ray bright rims of synchrotron radiation at their forward shocks. Thin rims require strong magnetic field amplification beyond simple shock compression if rim widths are only limited by electron energy losses. But, magnetic field damping behind the shock could produce similarly thin rims with less extreme field amplification. Variation of rim width with energy may thus discriminate between competing influences on rim widths. We measured rim widths around Tycho's supernova remnant in 5 energy bands using an archival 750 ks Chandra observation. Rims narrow with increasing energy and are well described by either loss-limited or damped scenarios, so X-ray rim width-energy dependence does not uniquely specify a model. But, radio counterparts to thin rims are not loss-limited and better reflect magnetic field structure. Joint radio and X-ray modeling favors magnetic damping in Tycho's SNR with damping lengths ~1--5% of remnant radius and magnetic field strengths ~50--400 $\mu$G assuming Bohm diffusion. X-ray rim widths are ~1% of remnant radius, somewhat smaller than inferred damping lengths. Electron energy losses are important in all models of X-ray rims, suggesting that the distinction between loss-limited and damped models is blurred in soft X-rays. All loss-limited and damping models require magnetic fields $\gtrsim$ 20 $\mu$G, affirming the necessity of magnetic field amplification beyond simple compression.