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

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.