A Cosmic Ray Acceleration Mechanism Based on Background Flow Velocity Inhomogeneities Yielding Power-law Spectra
In astrophysics, one significant challenge lies in understanding the acceleration of cosmic rays, which leads to the occurrence of a power law. In this article, momentum transport generated by the combined effects of pitch-angle diffusion and background flow velocity inhomogeneities is proposed to o...
Saved in:
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
|
| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ad93a8 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1841543729640374272 |
|---|---|
| author | J.-F. Wang G. Qin |
| author_facet | J.-F. Wang G. Qin |
| author_sort | J.-F. Wang |
| collection | DOAJ |
| description | In astrophysics, one significant challenge lies in understanding the acceleration of cosmic rays, which leads to the occurrence of a power law. In this article, momentum transport generated by the combined effects of pitch-angle diffusion and background flow velocity inhomogeneities is proposed to obtain a cosmic rays acceleration mechanism, starting from the well-known focused transport equation describing particle diffusion and acceleration. The inhomogeneities of background flow velocity are ubiquitous in the astrophysical environment. The equation for the isotropic part of the distribution function of charged energetic particles is derived, and its solution is obtained, demonstrating the form of momentum power laws of cosmic rays. In addition, if it is assumed that cosmic rays penetrate compressive MHD waves or turbulence, for quasi-steady states, the spectral index δ of the momentum power law spectrum of cosmic rays is found to be in the range [−5, −3], which includes the observed power law indices of galactic cosmic rays. The results obtained in this article demonstrate that the mechanism proposed in this article, along with shock acceleration, may also contribute to the acceleration of galactic cosmic rays. Furthermore, when momentum convection effect and higher-order momentum derivative terms are considered, the indices of power laws should be smaller than −5. This may explain the power laws of solar energetic particle events. |
| format | Article |
| id | doaj-art-f3c20f454749431dbf77f2edef9125f9 |
| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-f3c20f454749431dbf77f2edef9125f92025-01-13T07:35:10ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-019791810.3847/1538-4357/ad93a8A Cosmic Ray Acceleration Mechanism Based on Background Flow Velocity Inhomogeneities Yielding Power-law SpectraJ.-F. Wang0https://orcid.org/0000-0002-9586-093XG. Qin1https://orcid.org/0000-0002-3437-3716School of Science, Harbin Institute of Technology , Shenzhen, 518055, People's Republic of China ; qingang@hit.edu.cnSchool of Science, Harbin Institute of Technology , Shenzhen, 518055, People's Republic of China ; qingang@hit.edu.cn; Shenzhen Key Laboratory of Numerical Prediction for Space Storm, Harbin Institute of Technology , Shenzhen, 518055, People's Republic of ChinaIn astrophysics, one significant challenge lies in understanding the acceleration of cosmic rays, which leads to the occurrence of a power law. In this article, momentum transport generated by the combined effects of pitch-angle diffusion and background flow velocity inhomogeneities is proposed to obtain a cosmic rays acceleration mechanism, starting from the well-known focused transport equation describing particle diffusion and acceleration. The inhomogeneities of background flow velocity are ubiquitous in the astrophysical environment. The equation for the isotropic part of the distribution function of charged energetic particles is derived, and its solution is obtained, demonstrating the form of momentum power laws of cosmic rays. In addition, if it is assumed that cosmic rays penetrate compressive MHD waves or turbulence, for quasi-steady states, the spectral index δ of the momentum power law spectrum of cosmic rays is found to be in the range [−5, −3], which includes the observed power law indices of galactic cosmic rays. The results obtained in this article demonstrate that the mechanism proposed in this article, along with shock acceleration, may also contribute to the acceleration of galactic cosmic rays. Furthermore, when momentum convection effect and higher-order momentum derivative terms are considered, the indices of power laws should be smaller than −5. This may explain the power laws of solar energetic particle events.https://doi.org/10.3847/1538-4357/ad93a8Galactic cosmic raysMagnetic fieldsSolar energetic particles |
| spellingShingle | J.-F. Wang G. Qin A Cosmic Ray Acceleration Mechanism Based on Background Flow Velocity Inhomogeneities Yielding Power-law Spectra The Astrophysical Journal Galactic cosmic rays Magnetic fields Solar energetic particles |
| title | A Cosmic Ray Acceleration Mechanism Based on Background Flow Velocity Inhomogeneities Yielding Power-law Spectra |
| title_full | A Cosmic Ray Acceleration Mechanism Based on Background Flow Velocity Inhomogeneities Yielding Power-law Spectra |
| title_fullStr | A Cosmic Ray Acceleration Mechanism Based on Background Flow Velocity Inhomogeneities Yielding Power-law Spectra |
| title_full_unstemmed | A Cosmic Ray Acceleration Mechanism Based on Background Flow Velocity Inhomogeneities Yielding Power-law Spectra |
| title_short | A Cosmic Ray Acceleration Mechanism Based on Background Flow Velocity Inhomogeneities Yielding Power-law Spectra |
| title_sort | cosmic ray acceleration mechanism based on background flow velocity inhomogeneities yielding power law spectra |
| topic | Galactic cosmic rays Magnetic fields Solar energetic particles |
| url | https://doi.org/10.3847/1538-4357/ad93a8 |
| work_keys_str_mv | AT jfwang acosmicrayaccelerationmechanismbasedonbackgroundflowvelocityinhomogeneitiesyieldingpowerlawspectra AT gqin acosmicrayaccelerationmechanismbasedonbackgroundflowvelocityinhomogeneitiesyieldingpowerlawspectra AT jfwang cosmicrayaccelerationmechanismbasedonbackgroundflowvelocityinhomogeneitiesyieldingpowerlawspectra AT gqin cosmicrayaccelerationmechanismbasedonbackgroundflowvelocityinhomogeneitiesyieldingpowerlawspectra |