Particle acceleration at relativistic shock waves
Nov, 2011Citations per year
Abstract: (arXiv)
Relativistic sources, e.g. gamma-ray bursts, pulsar wind nebulae and powerful active galactic nuclei produce relativistic outflows that lead to the formation of collisionless shock waves, where particle acceleration is thought to take place. Our understanding of relativistic shock acceleration has improved in the past decade, thanks to the combination of analytical studies and high level numerical simulations. In ultra-relativistic shocks, particle acceleration is made difficult by the generically transverse magnetic field and large advection speed of the shocked plasma. Fast growing microturbulence is thus needed to make the Fermi process operative. It is thought, and numerical simulations support that view, that the penetration of supra-thermal particles in the shock precursor generates a magnetic turbulence which in turn produces the scattering process needed for particle acceleration through the Fermi mechanism. Through the comparison of the growth timescale of the microinstabilities in the shock precursor and the precursor crossing timescale, it is possible to delimit in terms of magnetization and shock Lorentz factor the region in which micro-turbulence may be excited, hence whether and how Fermi acceleration is triggered. These findings are summarized here and astrophysical consequences are drawn.Note:
- based on talks given at KIAA "Cosmic ray" workshop, at SF2A2011 and at WISAP2011; 16 pages, 1 figure. To be published in the proceedings of the WISAP 2011 Eilat meeting, eds M. Mond and P.-L. Sulem
- collisionless shock waves
- relativistic shock waves
- particle acceleration
- gamma-ray bursts
- particle: acceleration
- shock waves: relativistic
- magnetic field
- gamma ray: burst
- numerical calculations
- cosmic radiation
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