Particle Acceleration Controlled by Ambient Density in the Southwestern Rim of RCW 86

Abstract

The physics of particle acceleration at supernova remnant (SNR) shocks is one of the most intriguing problems in astrophysics. SNR RCW 86 provides a suitable environment for understanding the physics of particle acceleration because one can extract the information on both accelerated particles and acceleration environment in 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 ∼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 nonthermal parameters such as the power-law flux and index. From the decrease in flux over time of several nonthermal filaments, we estimate the magnetic field amplitudes to be ∼30–100 μG. 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 e as (power-law flux) and (power-law index) , and not or only weakly correlated 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.