Ultra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated Turbulence
Ultra-high-energy cosmic rays (UHECRs), particles characterized by energies exceeding 10 ^18 eV, are generally believed to be accelerated electromagnetically in high-energy astrophysical sources. One promising mechanism of UHECR acceleration is magnetized turbulence. We demonstrate from first princi...
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IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/ad955f |
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| author | Luca Comisso Glennys R. Farrar Marco S. Muzio |
| author_facet | Luca Comisso Glennys R. Farrar Marco S. Muzio |
| author_sort | Luca Comisso |
| collection | DOAJ |
| description | Ultra-high-energy cosmic rays (UHECRs), particles characterized by energies exceeding 10 ^18 eV, are generally believed to be accelerated electromagnetically in high-energy astrophysical sources. One promising mechanism of UHECR acceleration is magnetized turbulence. We demonstrate from first principles, using fully kinetic particle-in-cell simulations, that magnetically dominated turbulence accelerates particles on a short timescale, producing a power-law energy distribution with a rigidity-dependent, sharply defined cutoff well approximated by the form ${f}_{\mathrm{cut}}\left(E,{E}_{\mathrm{cut}}\right)={\rm{sech}} \left[{(E/{E}_{\mathrm{cut}})}^{2}\right]$ . Particle escape from the turbulent accelerating region is energy dependent, with t _esc ∝ E ^− ^δ and δ ∼ 1/3. The resulting particle flux from the accelerator follows ${dN}/{dEdt}\propto {E}^{-s}{\rm{sech}} \left[{(E/{E}_{\mathrm{cut}})}^{2}\right]$ , with s ∼ 2.1. We fit the Pierre Auger Observatory’s spectrum and composition measurements, taking into account particle interactions between acceleration and detection, and show that the turbulence-associated energy cutoff is well supported by the data, with the best-fitting spectral index being $s={2.1}_{-0.13}^{+0.06}$ . Our first-principles results indicate that particle acceleration by magnetically dominated turbulence may constitute the physical mechanism responsible for UHECR acceleration. |
| format | Article |
| id | doaj-art-1f1b36e7f4924595b3eefeb10bbe9e61 |
| institution | Kabale University |
| issn | 2041-8205 |
| language | English |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal Letters |
| spelling | doaj-art-1f1b36e7f4924595b3eefeb10bbe9e612025-01-03T12:24:40ZengIOP PublishingThe Astrophysical Journal Letters2041-82052024-01-019771L1810.3847/2041-8213/ad955fUltra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated TurbulenceLuca Comisso0https://orcid.org/0000-0001-8822-8031Glennys R. Farrar1https://orcid.org/0000-0003-2417-5975Marco S. Muzio2https://orcid.org/0000-0003-4615-5529Department of Physics, Columbia University , New York, NY 10027, USA; Department of Astronomy, Columbia University , New York, NY 10027, USA; Columbia Astrophysics Laboratory, Columbia University , New York, NY 10027, USACenter for Cosmology and Particle Physics, Department of Physics, New York University , New York, NY 10003, USADepartment of Physics, Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin , Madison, WI 53706, USA; Department of Physics, Pennsylvania State University , University Park, PA 16802, USA; Department of Astronomy and Astrophysics, Pennsylvania State University , University Park, PA 16802, USAUltra-high-energy cosmic rays (UHECRs), particles characterized by energies exceeding 10 ^18 eV, are generally believed to be accelerated electromagnetically in high-energy astrophysical sources. One promising mechanism of UHECR acceleration is magnetized turbulence. We demonstrate from first principles, using fully kinetic particle-in-cell simulations, that magnetically dominated turbulence accelerates particles on a short timescale, producing a power-law energy distribution with a rigidity-dependent, sharply defined cutoff well approximated by the form ${f}_{\mathrm{cut}}\left(E,{E}_{\mathrm{cut}}\right)={\rm{sech}} \left[{(E/{E}_{\mathrm{cut}})}^{2}\right]$ . Particle escape from the turbulent accelerating region is energy dependent, with t _esc ∝ E ^− ^δ and δ ∼ 1/3. The resulting particle flux from the accelerator follows ${dN}/{dEdt}\propto {E}^{-s}{\rm{sech}} \left[{(E/{E}_{\mathrm{cut}})}^{2}\right]$ , with s ∼ 2.1. We fit the Pierre Auger Observatory’s spectrum and composition measurements, taking into account particle interactions between acceleration and detection, and show that the turbulence-associated energy cutoff is well supported by the data, with the best-fitting spectral index being $s={2.1}_{-0.13}^{+0.06}$ . Our first-principles results indicate that particle acceleration by magnetically dominated turbulence may constitute the physical mechanism responsible for UHECR acceleration.https://doi.org/10.3847/2041-8213/ad955fParticle astrophysicsHigh energy astrophysicsCosmic raysPlasma astrophysicsPlasma physics |
| spellingShingle | Luca Comisso Glennys R. Farrar Marco S. Muzio Ultra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated Turbulence The Astrophysical Journal Letters Particle astrophysics High energy astrophysics Cosmic rays Plasma astrophysics Plasma physics |
| title | Ultra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated Turbulence |
| title_full | Ultra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated Turbulence |
| title_fullStr | Ultra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated Turbulence |
| title_full_unstemmed | Ultra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated Turbulence |
| title_short | Ultra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated Turbulence |
| title_sort | ultra high energy cosmic rays accelerated by magnetically dominated turbulence |
| topic | Particle astrophysics High energy astrophysics Cosmic rays Plasma astrophysics Plasma physics |
| url | https://doi.org/10.3847/2041-8213/ad955f |
| work_keys_str_mv | AT lucacomisso ultrahighenergycosmicraysacceleratedbymagneticallydominatedturbulence AT glennysrfarrar ultrahighenergycosmicraysacceleratedbymagneticallydominatedturbulence AT marcosmuzio ultrahighenergycosmicraysacceleratedbymagneticallydominatedturbulence |