Simulations of ion acceleration at nonrelativistic shocks. I. Acceleration efficiency
We use twodimensional and threedimensional hybrid (kinetic ionsfluid electrons) simulations to investigate particle acceleration and magnetic field amplification at nonrelativistic astrophysical shocks. We show that diffusive shock acceleration operates for quasiparallel configurations (i.e., when the background magnetic field is almost aligned with the shock normal) and, for large sonic and Alfvénic Mach numbers, produces universal powerlaw spectra ∝p {sup –4}, where p is the particle momentum. The maximum energy of accelerated ions increases with time, and it is only limited by finite box size and run time. Acceleration is mainly efficient for parallel and quasiparallel strong shocks, where 10%20% of the bulk kinetic energy can be converted to energetic particles and becomes ineffective for quasiperpendicular shocks. Also, the generation of magnetic turbulence correlates with efficient ion acceleration and vanishes for quasiperpendicular configurations. At very oblique shocks, ions can be accelerated via shock drift acceleration, but they only gain a factor of a few in momentum and their maximum energy does not increase with time. These findings are consistent with the degree of polarization and the morphology of the radio and Xray synchrotron emission observed, for instance, in the remnant of SN 1006. We also discuss the transition from thermal tomore »
 Authors:

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^{[1]}
 Department of Astrophysical Sciences, Princeton University, 4 Ivy Ln., Princeton, NJ 08544 (United States)
 Publication Date:
 OSTI Identifier:
 22351597
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Astrophysical Journal; Journal Volume: 783; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; ALFVEN WAVES; ASTROPHYSICS; CONFIGURATION; ELECTRONS; EMISSION; GAIN; IONS; MAGNETIC FIELDS; POLARIZATION; RELATIVISTIC RANGE; SHOCK WAVES; SIMULATION; SPECTRA; SUPERNOVA REMNANTS; SYNCHROTRON RADIATION; THREEDIMENSIONAL CALCULATIONS; TURBULENCE; TWODIMENSIONAL CALCULATIONS; X RADIATION