Speed-dependent Threshold for Electron Injection into Diffusive Shock Acceleration
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866918054660669440 |
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| author | Gupta, Siddhartha Caprioli, Damiano Spitkovsky, Anatoly |
| author_facet | Gupta, Siddhartha Caprioli, Damiano Spitkovsky, Anatoly |
| contents | Finding the injection threshold for diffusive shock acceleration (DSA) of electrons in collisionless shocks has been a longstanding unsolved problem. Using first-principles kinetic simulations, we identify the conditions for electron injection into DSA and quantify the evolution of the nonthermal tail in self-generated electromagnetic turbulence. By analyzing electron trajectories and their momentum gain during shock-recrossing cycles, we demonstrate that electrons start participating in DSA when their speed is large enough to overrun the shock. We develop a minimal model showing that speed-dependent injection reproduces nonthermal electron spectra observed in kinetic simulations. Our findings establish a new criterion for electron DSA, which has broad implications for the nonthermal emission of shock-powered space/astrophysical systems. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2506_09134 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Speed-dependent Threshold for Electron Injection into Diffusive Shock Acceleration Gupta, Siddhartha Caprioli, Damiano Spitkovsky, Anatoly High Energy Astrophysical Phenomena Plasma Physics Finding the injection threshold for diffusive shock acceleration (DSA) of electrons in collisionless shocks has been a longstanding unsolved problem. Using first-principles kinetic simulations, we identify the conditions for electron injection into DSA and quantify the evolution of the nonthermal tail in self-generated electromagnetic turbulence. By analyzing electron trajectories and their momentum gain during shock-recrossing cycles, we demonstrate that electrons start participating in DSA when their speed is large enough to overrun the shock. We develop a minimal model showing that speed-dependent injection reproduces nonthermal electron spectra observed in kinetic simulations. Our findings establish a new criterion for electron DSA, which has broad implications for the nonthermal emission of shock-powered space/astrophysical systems. |
| title | Speed-dependent Threshold for Electron Injection into Diffusive Shock Acceleration |
| topic | High Energy Astrophysical Phenomena Plasma Physics |
| url | https://arxiv.org/abs/2506.09134 |