Particle acceleration controlled by ambient density in the southwestern rim of RCW 86

TL;DR

This study investigates how ambient density influences particle acceleration in the supernova remnant RCW 86 by analyzing X-ray proper motions, spectral properties, and magnetic fields, revealing a strong correlation between synchrotron emission and ambient density.

Contribution

It provides new insights into the relationship between ambient density and particle acceleration efficiency, emphasizing the role of shock-cloud interactions in magnetic turbulence enhancement.

Findings

Synchrotron emission correlates with ambient density as flux ∝ n_e^{1.0 ± 0.2}.

Magnetic field amplitudes estimated to be 30–100 μG.

Inward-moving filaments are likely reflected shocks, not reverse shocks.

Abstract

Particle acceleration physics at supernova remnant (SNR) shocks is one of the most intriguing problems in astrophysics. SNR RCW~86 provides a suitable environment for understanding the particle acceleration physics because one can extract the information of both accelerated particles and acceleration environment at the same regions through the bright X-ray emission. In this work, we study X-ray proper motions and spectral properties of the southwestern region of RCW~86. The proper motion velocities are found to be $\sim 300$--2000~km~s$^{-1}$ at a distance of 2.8~kpc. We find two inward-moving filaments, which are more likely reflected shocks rather than reverse shocks. Based on the X-ray spectroscopy, we evaluate thermal parameters such as the ambient density and temperature, and non-thermal parameters such as the power-law flux and index. From the flux decrease in time of several non-thermal filaments, we estimate the magnetic field amplitudes to be $\sim 30$--100~$\mu$G. Gathering the physical parameters, we then investigate parameter correlations. We find that the synchrotron emission from thermal-dominated filaments is correlated with the ambient density $n_{\rm e}$ as $\text{(power-law flux)} \propto n_{\rm e}^{1.0 \pm 0.2}$ and $\text{(power-law index)} \propto n_{\rm e}^{0.38 \pm 0.10}$, not or only weakly with the shock velocity and shock obliquity. As an interpretation, we propose a shock-cloud interaction scenario, where locally enhanced magnetic turbulence levels have a great influence on local acceleration conditions.