Cosmic-Ray Acceleration Efficiency vs Temperature Equilibration: the Case of SNR 0509-67.5

TL;DR

This study investigates the relationship between cosmic-ray acceleration efficiency and temperature equilibration in the supernova remnant SNR 0509-67.5, revealing significant cosmic-ray influence on shock properties and challenging existing models.

Contribution

It provides observational evidence linking cosmic-ray pressure to temperature equilibration in supernova shocks, highlighting the need to revise current models for fast shock physics.

Findings

Proton temperatures are lower than expected for shock velocities, indicating cosmic-ray pressure influence.

The plasma behind the NE shock shows over 20% thermal equilibrium, conflicting with existing models.

Cosmic-ray pressure behind the shock is at least 7%, affecting shock dynamics.

Abstract

We study the 0509-67.5 supernova remnant in the Large Magellanic Cloud with the VLT/FORS2 spectrograph. We detect a broad component in the H-alpha emission with a FWHM of 2680 \pm 70 km/s and 3900 \pm 800 km/s for the southwest (SW) and northeast (NE) shocks respectively. For the SW, the proton temperature appears to be too low for the shock velocity, which we attribute to a cosmic-ray pressure behind the shock front of at least 20% of the total pressure. For the NE, the post-shock proton temperature and the shock velocity are compatible, only if the plasma behind the shock front has a degree of thermal equilibrium of over 20%, which is at odds with current models for temperature equilibration behind fast shocks, which do not accelerate cosmic rays. If we assume the electron temperature to be less than 10% of the proton temperature, we find a post-shock cosmic-ray pressure of at least 7%.