Cosmic‐Ray Acceleration at Ultrarelativistic Shock Waves: Effects of Downstream Short‐Wave Turbulence
- 20 October 2006
- journal article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 650 (2), 1020-1027
- https://doi.org/10.1086/506901
Abstract
The present paper is the last of a series studying the first-order Fermi acceleration processes at relativistic shock waves with the method of Monte Carlo simulations applied to shocks propagating in realistically modeled turbulent magnetic fields. The model of the background magnetic field structure of Niemiec & Ostrowski (2004, 2006) has been augmented here by a large-amplitude short-wave downstream component, imitating that generated by plasma instabilities at the shock front. Following Niemiec & Ostrowski (2006), we have considered ultrarelativistic shocks with the mean magnetic field oriented both oblique and parallel to the shock normal. For both cases simulations have been performed for different choices of magnetic field perturbations, represented by various wave power spectra within a wide wavevector range. The results show that the introduction of the short-wave component downstream of the shock is not sufficient to produce power-law particle spectra with the "universal" spectral index 4.2. On the contrary, concave spectra with cutoffs are preferentially formed, the curvature and cutoff energy being dependent on the properties of turbulence. Our results suggest that the electromagnetic emission observed from astrophysical sites with relativistic jets, e.g. AGN and GRBs, is likely generated by particles accelerated in processes other than the widely invoked first-order Fermi mechanism.Comment: 9 pages, 8 figures, submitted to ApKeywords
This publication has 31 references indexed in Scilit:
- Diffusive shock acceleration in unmodified relativistic, oblique shocksAstroparticle Physics, 2004
- Magnetic Field Generation in Collisionless Shocks: Pattern Growth and TransportThe Astrophysical Journal, 2004
- Particle acceleration through multiple conversions from a charged into a neutral state and backPhysical Review D, 2003
- Nonlinear particle acceleration in relativistic shocksAstroparticle Physics, 2002
- Particle acceleration by ultrarelativistic shocks: theory and simulationsMonthly Notices of the Royal Astronomical Society, 2001
- Ultra-high-energy cosmic ray acceleration by relativistic blast wavesMonthly Notices of the Royal Astronomical Society, 1999
- Energy Spectra of Cosmic Rays Accelerated at Ultrarelativistic Shock WavesPhysical Review Letters, 1998
- The acceleration time-scale for first-order Fermi acceleration in relativistic shock wavesMonthly Notices of the Royal Astronomical Society, 1996
- Shock-drift particle acceleration in superluminal shocks - A model for hot spots in extragalactic radio sourcesThe Astrophysical Journal, 1990
- Relativistic shocks and particle accelerationMonthly Notices of the Royal Astronomical Society, 1988