SLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical Shocks
Short large-amplitude magnetic structures (SLAMS) are frequently detected during spacecraft crossings over Earth's bow shock. We investigate the existence of such structures at astrophysical shocks, where they could result from the steepening of cosmic-ray (CR) driven waves. Using kinetic parti...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ade05f |
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| author | Vladimir Zeković Anatoly Spitkovsky Zachary Hemler |
| author_facet | Vladimir Zeković Anatoly Spitkovsky Zachary Hemler |
| author_sort | Vladimir Zeković |
| collection | DOAJ |
| description | Short large-amplitude magnetic structures (SLAMS) are frequently detected during spacecraft crossings over Earth's bow shock. We investigate the existence of such structures at astrophysical shocks, where they could result from the steepening of cosmic-ray (CR) driven waves. Using kinetic particle-in-cell simulations, we study the growth of SLAMS and the appearance of associated transient shocks in the upstream region of parallel, nonrelativistic, high-Mach-number collisionless shocks. We find that high-energy CRs significantly enhance the transverse magnetic field within SLAMS, producing highly inclined field lines. As SLAMS are advected toward the shock, these field lines form an intermittent superluminal configuration that traps magnetized electrons at fast shocks. Due to their oscillatory nature, SLAMS are periodically separated by subluminal gaps with lower transverse magnetic field strength. In these regions, electrons diffuse and accelerate by bouncing between the shock and the approaching SLAMS' region through a mechanism that we call quasi-periodic shock acceleration (QSA). We analytically derive the distribution of electrons accelerated via QSA, f ( p ) ∼ p ^[−4.7,−5.7] , which agrees well with the simulation spectra. We find that the electron power law remains steep until the end of our longest runs, providing a possible explanation for the steep electron spectra observed at least up to GeV energies in young and fast supernova remnants. |
| format | Article |
| id | doaj-art-c6a84777f4a04cffb77bd839f2b75b66 |
| 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-c6a84777f4a04cffb77bd839f2b75b662025-08-20T03:16:47ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198814010.3847/1538-4357/ade05fSLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical ShocksVladimir Zeković0https://orcid.org/0000-0002-4985-3253Anatoly Spitkovsky1https://orcid.org/0000-0001-9179-9054Zachary Hemler2https://orcid.org/0000-0002-0799-0225Department of Astronomy, Faculty of Mathematics, University of Belgrade , Studentski trg 16, 11000 Belgrade, Serbia ; vladimir.zekovic@matf.bg.ac.rs; Department of Astrophysical Sciences, Princeton University , Princeton, NJ 08544, USADepartment of Astrophysical Sciences, Princeton University , Princeton, NJ 08544, USADepartment of Astrophysical Sciences, Princeton University , Princeton, NJ 08544, USAShort large-amplitude magnetic structures (SLAMS) are frequently detected during spacecraft crossings over Earth's bow shock. We investigate the existence of such structures at astrophysical shocks, where they could result from the steepening of cosmic-ray (CR) driven waves. Using kinetic particle-in-cell simulations, we study the growth of SLAMS and the appearance of associated transient shocks in the upstream region of parallel, nonrelativistic, high-Mach-number collisionless shocks. We find that high-energy CRs significantly enhance the transverse magnetic field within SLAMS, producing highly inclined field lines. As SLAMS are advected toward the shock, these field lines form an intermittent superluminal configuration that traps magnetized electrons at fast shocks. Due to their oscillatory nature, SLAMS are periodically separated by subluminal gaps with lower transverse magnetic field strength. In these regions, electrons diffuse and accelerate by bouncing between the shock and the approaching SLAMS' region through a mechanism that we call quasi-periodic shock acceleration (QSA). We analytically derive the distribution of electrons accelerated via QSA, f ( p ) ∼ p ^[−4.7,−5.7] , which agrees well with the simulation spectra. We find that the electron power law remains steep until the end of our longest runs, providing a possible explanation for the steep electron spectra observed at least up to GeV energies in young and fast supernova remnants.https://doi.org/10.3847/1538-4357/ade05fShocksCosmic raysAstronomical simulationsSupernova remnantsInterstellar medium |
| spellingShingle | Vladimir Zeković Anatoly Spitkovsky Zachary Hemler SLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical Shocks The Astrophysical Journal Shocks Cosmic rays Astronomical simulations Supernova remnants Interstellar medium |
| title | SLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical Shocks |
| title_full | SLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical Shocks |
| title_fullStr | SLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical Shocks |
| title_full_unstemmed | SLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical Shocks |
| title_short | SLAMS-propelled Electron Acceleration at High-Mach-number Astrophysical Shocks |
| title_sort | slams propelled electron acceleration at high mach number astrophysical shocks |
| topic | Shocks Cosmic rays Astronomical simulations Supernova remnants Interstellar medium |
| url | https://doi.org/10.3847/1538-4357/ade05f |
| work_keys_str_mv | AT vladimirzekovic slamspropelledelectronaccelerationathighmachnumberastrophysicalshocks AT anatolyspitkovsky slamspropelledelectronaccelerationathighmachnumberastrophysicalshocks AT zacharyhemler slamspropelledelectronaccelerationathighmachnumberastrophysicalshocks |