Bi-directional streaming of particles accelerated at the STEREO-A shock on 2008 March 9
Abstract
We present an interpretation of anisotropy and intensity of supra-thermal ions near a fast quasi-perpendicular reverse shock measured by Solar Terrestrial Relations Observatory Ahead (ST-A) on 2008 March 9. The measured intensity profiles of the supra-thermal particles exhibit an enhancement, or 'spike', at the time of the shock arrival and pitch-angle anisotropies before the shock arrival are bi-modal, jointly suggesting trapping of near-scatter-free ions along magnetic field lines that intersect the shock at two locations. We run test-particle simulations with pre-existing upstream magnetostatic fluctuations advected across the shock. The measured bi-modal upstream anisotropy, the nearly field-aligned anisotropies up to ~15 min upstream of the shock, as well as the 'pancake-like' anisotropies up to ~10 min downstream of the shock are well reproduced by the simulations. These results, in agreement with earlier works, suggest a dominant role of the large-scale structure (100s of supra-thermal proton gyroradii) of the magnetic field in forging the early-on particle acceleration at shocks.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2020
- DOI:
- 10.1093/mnras/staa3021
- arXiv:
- arXiv:2009.13662
- Bibcode:
- 2020MNRAS.499.2087F
- Keywords:
-
- acceleration of particles;
- shock waves;
- turbulence;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics;
- Physics - Space Physics
- E-Print:
- 7 pages, 4 figures, MNRAS in press