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Peer-reviewedCC BY 4.0The Astrophysical Journal

Modulation of Galactic Cosmic Rays in the Very Local Interstellar Medium: Energy and Species Dependence

  • Ming Zhang1
  • Nikolai Pogorelov2
  • Federico Fraternale2
  • Alan C. Cummings3
  1. 1150 W. University Blvd.
  2. 2The University of Alabama in Huntsville
  3. 3California Institute of Technology
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Abstract

Observations from Voyager 1 in the very local interstellar medium (VLISM) have revealed long-lasting events of anisotropic fluxes in Galactic cosmic-ray (GCR) protons, but much less so in electrons. In this work, we extend our previous numerical model of cosmic-ray modulation by heliospheric plasma disturbances propagating into the VLISM to treat the transport of both protons and electrons. We simulate the modulation of 100 MeV protons and 4 MeV electrons in response to pressure pulses, magnetic compressions, and rarefactions propagating through the outer heliosheath. The simulations show that adiabatic cooling associated with trapping within the propagating structure can produce strong modulation of protons near a 90 ∘ pitch angle. In contrast, the faster, ultrarelativistic electrons at ∼4 MeV undergo relatively rapid pitch-angle scattering, which reduces the effectiveness of trapping and energy loss. As a result, electron intensities are less strongly modulated, whereas the proton distributions develop a pronounced decrease near a 90 ∘ pitch angle. Both GCR electrons and protons experience drift acceleration at the shock front, producing enhanced particle intensities in the foreshock region and at the shock itself.

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Cite

BibTeXRIS
BibTeX
@article{zhang2026modulation,
  title = {{Modulation of Galactic Cosmic Rays in the Very Local Interstellar Medium: Energy and Species Dependence}},
  author = {Ming Zhang and Nikolai Pogorelov and Federico Fraternale and Alan C. Cummings},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aeac56},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aeac56},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Modulation of Galactic Cosmic Rays in the Very Local Interstellar Medium: Energy and Species Dependence
AU  - Ming Zhang
AU  - Nikolai Pogorelov
AU  - Federico Fraternale
AU  - Alan C. Cummings
PY  - 2026
DA  - 2026/10/27
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aeac56
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aeac56
AB  - Observations from Voyager 1 in the very local interstellar medium (VLISM) have revealed long-lasting events of anisotropic fluxes in Galactic cosmic-ray (GCR) protons, but much less so in electrons. In this work, we extend our previous numerical model of cosmic-ray modulation by heliospheric plasma disturbances propagating into the VLISM to treat the transport of both protons and electrons. We simulate the modulation of 100 MeV protons and 4 MeV electrons in response to pressure pulses, magnetic compressions, and rarefactions propagating through the outer heliosheath. The simulations show that adiabatic cooling associated with trapping within the propagating structure can produce strong modulation of protons near a 90 ∘ pitch angle. In contrast, the faster, ultrarelativistic electrons at ∼4 MeV undergo relatively rapid pitch-angle scattering, which reduces the effectiveness of trapping and energy loss. As a result, electron intensities are less strongly modulated, whereas the proton distributions develop a pronounced decrease near a 90 ∘ pitch angle. Both GCR electrons and protons experience drift acceleration at the shock front, producing enhanced particle intensities in the foreshock region and at the shock itself.
SN  - 1538-4357
SN  - 0004-637X
ER  -