Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration

Raptis, Savvas; Lalti, Ahmad; Lindberg, Martin; Turner, Drew L.; Caprioli, Damiano; Burch, James L.

doi:10.6082/5kkp3-9xy41

Published January 13, 2025 | Version v1

Journal article Open

Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration

1. Johns Hopkins University
2. Northumbria University
3. KTH Royal Institute of Technology
4. University of Chicago
5. Southwest Research Institute

Collisionless shock waves, found in supernova remnants, interstellar, stellar, and planetary environments, and laboratories, are one of nature's most powerful particle accelerators. This study combines in situ satellite measurements with recent theoretical developments to establish a reinforced shock acceleration model for relativistic electrons. Our model incorporates transient structures, wave-particle interactions, and variable stellar wind conditions, operating collectively in a multiscale set of processes. We show that the electron injection threshold is on the order of suprathermal range, obtainable through multiple different phenomena abundant in various plasma environments. Our analysis demonstrates that a typical shock can consistently accelerate electrons into very high (relativistic) energy ranges, refining our comprehension of shock acceleration while providing insight on the origin of electron cosmic rays.

Data availability

The MMS data are archived at https://lasp.colorado.edu/mms/sdc/public/. The THEMIS/ARTEMIS data can be found at https://themis.ssl.berkeley.edu/data_products/index.php, while the OMNIweb data is accessed through https://spdf.gsfc.nasa.gov/pub/data/omni/. Information about the level, calibration, and instrumentation used for each quantity can be found in the method, subsection data. All calculations shown and reported in this work are done with the open-access data available from each mission as a level-2 calibrated dataset. The post-processed data supporting the findings of this study, specifically the non-time series data (i.e., Figs. 2i and 3), are provided as source data to facilitate easier reproducibility. The remaining post-processed data are available from the corresponding author upon request. Source data are provided in this paper.

The analysis of the work was done via the PySPEDAS (https://github.com/spedas/pyspedas/tree/master), SPEDAS (http://spedas.org/blog/ and IRFU-Matlab (https://github.com/irfu/irfu-matlab/tree/master) libraries. Specifically, PySPEDAS was used to download the observations and IRFU-Matlab to analyze and process the files for the plots and the analysis shown in the manuscript. One can access the version of the codes used along with instructions on how to reproduce each figure and table of our work on the associated Zenodo repository https://zenodo.org/records/14048045 or directly from the GitHub repository https://github.com/SavvasRaptis/Relativistic-Electrons-Foreshock. Alternatively, all the software listed above is openly available through their official repository. In addition, we made use of the machine learning code openly available on ref. 38 and on the hosting website of the corresponding author https://ecamporeale.github.io/codes.html by following the Solar Wind Classification MATLAB code. Specifically, following https://ecamporeale.github.io/software/OMNI2_classification.dat provides the training dataset for the code, https://ecamporeale.github.io/software/classify_solar_wind.m shows a working code example, and https://ecamporeale.github.io/software/parameters_classification.mat contains the parameters required to run the model. Finally, we used a 3D bow shock model, openly described in ref. 69. Its implementation in MATLAB is straightforward and can be made available from the corresponding author upon request.

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