### Abstract

We use nondiffusive, nonrelativistic, test-particle numerical simulations to address the physics of particle acceleration by collisionless shocks. We focus on the importance of the shock normal angle, (θ_{Bn}), in determining the energy spectrum of the accelerated particles. For reasonable parameters, we find that the injection velocity is weakly dependent on the mean shock normal angle and that low-energy particles are readily accelerated to high energies irrespective of 〈θ_{Bn}〉. Our results are applicable for shocks that are nearly planar on scales larger than the coherence scale of the upstream magnetic turbulence and for particles whose gyroradii are smaller than this scale. We confirm previous results showing that the acceleration rate is larger for nearly perpendicular shocks compared to parallel shocks. However, we also find that the acceleration rate at parallel shocks moving through large-scale magnetic fluctuations is larger than that predicted by simple first-order Fermi acceleration. Our results can be understood in terms of the nature of the large-scale fluctuations and their effect on particle transport.

Original language | English (US) |
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Pages (from-to) | 765-772 |

Number of pages | 8 |

Journal | Astrophysical Journal |

Volume | 624 |

Issue number | 2 I |

DOIs | |

State | Published - May 10 2005 |

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### Keywords

- Acceleration of particles
- Cosmic rays
- Methods: numerical
- Shock waves

### ASJC Scopus subject areas

- Space and Planetary Science

### Cite this

**Particle acceleration at shocks moving through an irregular magnetic field.** / Giacalone, Joe.

Research output: Contribution to journal › Article

*Astrophysical Journal*, vol. 624, no. 2 I, pp. 765-772. https://doi.org/10.1086/429265

}

TY - JOUR

T1 - Particle acceleration at shocks moving through an irregular magnetic field

AU - Giacalone, Joe

PY - 2005/5/10

Y1 - 2005/5/10

N2 - We use nondiffusive, nonrelativistic, test-particle numerical simulations to address the physics of particle acceleration by collisionless shocks. We focus on the importance of the shock normal angle, (θBn), in determining the energy spectrum of the accelerated particles. For reasonable parameters, we find that the injection velocity is weakly dependent on the mean shock normal angle and that low-energy particles are readily accelerated to high energies irrespective of 〈θBn〉. Our results are applicable for shocks that are nearly planar on scales larger than the coherence scale of the upstream magnetic turbulence and for particles whose gyroradii are smaller than this scale. We confirm previous results showing that the acceleration rate is larger for nearly perpendicular shocks compared to parallel shocks. However, we also find that the acceleration rate at parallel shocks moving through large-scale magnetic fluctuations is larger than that predicted by simple first-order Fermi acceleration. Our results can be understood in terms of the nature of the large-scale fluctuations and their effect on particle transport.

AB - We use nondiffusive, nonrelativistic, test-particle numerical simulations to address the physics of particle acceleration by collisionless shocks. We focus on the importance of the shock normal angle, (θBn), in determining the energy spectrum of the accelerated particles. For reasonable parameters, we find that the injection velocity is weakly dependent on the mean shock normal angle and that low-energy particles are readily accelerated to high energies irrespective of 〈θBn〉. Our results are applicable for shocks that are nearly planar on scales larger than the coherence scale of the upstream magnetic turbulence and for particles whose gyroradii are smaller than this scale. We confirm previous results showing that the acceleration rate is larger for nearly perpendicular shocks compared to parallel shocks. However, we also find that the acceleration rate at parallel shocks moving through large-scale magnetic fluctuations is larger than that predicted by simple first-order Fermi acceleration. Our results can be understood in terms of the nature of the large-scale fluctuations and their effect on particle transport.

KW - Acceleration of particles

KW - Cosmic rays

KW - Methods: numerical

KW - Shock waves

UR - http://www.scopus.com/inward/record.url?scp=19844375721&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=19844375721&partnerID=8YFLogxK

U2 - 10.1086/429265

DO - 10.1086/429265

M3 - Article

AN - SCOPUS:19844375721

VL - 624

SP - 765

EP - 772

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 I

ER -