Colliding-Wind Binaries as a Source of TeV Cosmic Rays

In addition to the gamma-ray binaries which contain a compact object, high energy (HE) and very high energy (VHE) 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 non-thermal 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.