Particle acceleration and non-thermal emission in colliding-wind binary systems

Abstract

We present a model for the creation of non-thermal particles via diffusive shock acceleration in a colliding-wind binary. Our model accounts for the oblique nature of the global shocks bounding the wind-wind collision region and the finite velocity of the scattering centres to the gas. It also includes magnetic field amplification by the cosmic ray induced streaming instability and the dynamical back reaction of the amplified field. We assume that the injection of the ions and electrons is independent of the shock obliquity and that the scattering centres move relative to the fluid at the Alfvén velocity (resulting in steeper non-thermal particle distributions). We find that the Mach number, Alfvénic Mach number, and transverse field strength vary strongly along and between the shocks, resulting in significant and non-linear variations in the particle acceleration efficiency and shock nature (turbulent vs. non-turbulent). We find much reduced compression ratios at the oblique shocks in most of our models compared to our earlier work, though total gas compression ratios that exceed 20 can still be obtained in certain situations. We also investigate the dependence of the non-thermal emission on the stellar separation and determine when emission from secondary electrons becomes important. We finish by applying our model to WR 146, one of the brightest colliding wind binaries in the radio band. We are able to match the observed radio emission and find that roughly 30 per cent of the wind power at the shocks is channelled into non-thermal particles.

22 pages, 19 figures, accepted for publication in MNRAS

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Cited by in corpus (14)

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• Evidence for non-thermal X-ray emission from the double WR colliding-wind binary Apep
• X-ray emission of massive stars and their winds
• Radio emission from colliding outflows in high-mass X-ray binaries with strongly magnetized neutron stars
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• The non-thermal emission from the colliding-wind binary Apep
• The colliding-wind binary HD 168112
• Investigating the Role of Pre-supernova Massive Stars in the Acceleration of Galactic Cosmic Rays
• Limits on the non-thermal emission of the WR-WR system Apep
• Radio Spectral Energy Distributions for Single Massive Star Winds with Free-Free and Synchrotron Emission