Colliding-Wind Binaries as a Source of TeV Cosmic Rays

TL;DR

This study uses 3D magnetohydrodynamic simulations to demonstrate that colliding-wind binaries can accelerate particles to TeV energies, contributing to our understanding of cosmic ray sources.

Contribution

First comprehensive 3D MHD simulations coupled with particle kinematics showing particle acceleration in colliding-wind binaries.

Findings

Colliding-wind binaries produce nonthermal particles up to TeV energies.

Magnetic field amplification is crucial for particle acceleration.

Acceleration occurs rapidly in turbulent, magnetized shock regions.

Abstract

In addition to gamma-ray binaries which contain a compact object, high-energy and very high-energy gamma rays have also been detected from colliding-wind binaries. The collision of the winds produces two strong shock fronts, one for each wind, both surrounding a shock region of compressed and heated plasma, where particles are accelerated to very high energies. Magnetic field is also amplified in the shocked region on which the acceleration of particles greatly depends. In this work, we performed full three-dimensional magnetohydrodynamic simulations of colliding winds coupled to a code that evolves the kinematics of passive charged test particles subject to the plasma fluctuations. After the run of a large ensemble of test particles with initial thermal distributions, we show that such shocks produce a nonthermal population (nearly 1% of total particles) of few tens of GeVs up to few TeVs, depending on the initial magnetization level of the stellar winds. We were able to determine the loci of fastest acceleration, in the range of MeV/s to GeV/s, to be related to the turbulent plasma with amplified magnetic field of the shock. These results show that colliding-wind binaries are indeed able to produce a significant population of high-energy particles, in relatively short timescales, compared to the dynamical and diffusion timescales.