Electron Acceleration at Shock Ripples: Role of Pitch-angle Diffusion
Suprathermal electrons are routinely observed in interplanetary space. At higher energies, there are in-situ evidences that shocks, both interplanetary shocks, often driven by fast coronal mass ejections, and terrestrial bow shocks, can accelerate electrons up to transrelativistic energies (∼MeVs)....
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ade23e |
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| author | Y. D. Xu G. Li S. Yao |
| author_facet | Y. D. Xu G. Li S. Yao |
| author_sort | Y. D. Xu |
| collection | DOAJ |
| description | Suprathermal electrons are routinely observed in interplanetary space. At higher energies, there are in-situ evidences that shocks, both interplanetary shocks, often driven by fast coronal mass ejections, and terrestrial bow shocks, can accelerate electrons up to transrelativistic energies (∼MeVs). The acceleration mechanism responsible for these energetic electrons is still under debate. In this work, we study the effects of large-scale shock ripples on electron acceleration at a quasi-perpendicular shock in a 2D system. For tractability of the numerical simulation, we consider the scenario where the magnetic field line contains ripples, and the shock is assumed planar and piecewise. The propagation of gyrophase-averaged electrons is governed by the focused transport equation, where the effect of the turbulent magnetic field is modeled by the pitch-angle diffusion, described by the quasi-linear theory. A Monte Carlo simulation on the equivalent time-forward Itô stochastic differential equation is performed within a periodic box to obtain the phase-space distribution function of the accelerated electrons. Our model predicts power-law energy spectra with a cutoff at high-energy ends, whereas their spectral indices are softer than those predicted by the diffusive shock acceleration theory. We demonstrate that, with a suitable choice of pitch-angle diffusion strength, a small fraction of electrons can experience magnetic traps in multiple ripples along the shock surface, boosting their energies to ∼MeVs. Our results therefore provide a framework for a better understanding of relativistic electron events associated with shocks within the heliosphere. |
| format | Article |
| id | doaj-art-e95db23d52ce487195425e9eeff50c85 |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-e95db23d52ce487195425e9eeff50c852025-08-20T03:12:27ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198816710.3847/1538-4357/ade23eElectron Acceleration at Shock Ripples: Role of Pitch-angle DiffusionY. D. Xu0https://orcid.org/0000-0003-4055-5695G. Li1https://orcid.org/0000-0003-4695-8866S. Yao2https://orcid.org/0000-0003-4267-0486School of Geophysics and Information Technology, China University of Geosciences , Beijing, People’s Republic of China ; yaoshuo@cugb.edu.cnState Key Laboratory of Lunar and Planetary Sciences and CNSA Macau Center for Space Exploration and Science, Macau University of Science and Technology , Macau, People’s Republic of China ; gli@must.edu.moSchool of Geophysics and Information Technology, China University of Geosciences , Beijing, People’s Republic of China ; yaoshuo@cugb.edu.cnSuprathermal electrons are routinely observed in interplanetary space. At higher energies, there are in-situ evidences that shocks, both interplanetary shocks, often driven by fast coronal mass ejections, and terrestrial bow shocks, can accelerate electrons up to transrelativistic energies (∼MeVs). The acceleration mechanism responsible for these energetic electrons is still under debate. In this work, we study the effects of large-scale shock ripples on electron acceleration at a quasi-perpendicular shock in a 2D system. For tractability of the numerical simulation, we consider the scenario where the magnetic field line contains ripples, and the shock is assumed planar and piecewise. The propagation of gyrophase-averaged electrons is governed by the focused transport equation, where the effect of the turbulent magnetic field is modeled by the pitch-angle diffusion, described by the quasi-linear theory. A Monte Carlo simulation on the equivalent time-forward Itô stochastic differential equation is performed within a periodic box to obtain the phase-space distribution function of the accelerated electrons. Our model predicts power-law energy spectra with a cutoff at high-energy ends, whereas their spectral indices are softer than those predicted by the diffusive shock acceleration theory. We demonstrate that, with a suitable choice of pitch-angle diffusion strength, a small fraction of electrons can experience magnetic traps in multiple ripples along the shock surface, boosting their energies to ∼MeVs. Our results therefore provide a framework for a better understanding of relativistic electron events associated with shocks within the heliosphere.https://doi.org/10.3847/1538-4357/ade23eShocksInterplanetary particle accelerationSolar energetic particles |
| spellingShingle | Y. D. Xu G. Li S. Yao Electron Acceleration at Shock Ripples: Role of Pitch-angle Diffusion The Astrophysical Journal Shocks Interplanetary particle acceleration Solar energetic particles |
| title | Electron Acceleration at Shock Ripples: Role of Pitch-angle Diffusion |
| title_full | Electron Acceleration at Shock Ripples: Role of Pitch-angle Diffusion |
| title_fullStr | Electron Acceleration at Shock Ripples: Role of Pitch-angle Diffusion |
| title_full_unstemmed | Electron Acceleration at Shock Ripples: Role of Pitch-angle Diffusion |
| title_short | Electron Acceleration at Shock Ripples: Role of Pitch-angle Diffusion |
| title_sort | electron acceleration at shock ripples role of pitch angle diffusion |
| topic | Shocks Interplanetary particle acceleration Solar energetic particles |
| url | https://doi.org/10.3847/1538-4357/ade23e |
| work_keys_str_mv | AT ydxu electronaccelerationatshockripplesroleofpitchanglediffusion AT gli electronaccelerationatshockripplesroleofpitchanglediffusion AT syao electronaccelerationatshockripplesroleofpitchanglediffusion |