Influence of interstellar environment near the solar system on cosmic-ray spectra and dipole anisotropy

TL;DR

This paper presents a three-component model explaining how the local interstellar environment influences cosmic-ray spectra and anisotropy, addressing longstanding questions about cosmic ray behavior near the solar system.

Contribution

It introduces a detailed model linking local interstellar conditions to cosmic-ray anisotropy, supported by observational data and predictions for future measurements.

Findings

The model explains the energy dependence of cosmic ray dipole anisotropy.

Dipole amplitude and angle are sensitive to heliosphere and interstellar cloud velocities.

Future measurements can test the model's predictions.

Abstract

Properties of interstellar environment near the solar system have been probed by missions like IBEX, Voyager over the last two decades. Although it has been well recognized that properties of cosmic rays up to the PeV energy can be affected by the local interstellar environment, detailed modeling has not been done. We show that a three component model for the cosmic ray proton and helium spectra from GV to several PV can naturally explain the energy dependence of the dipole anisotropy of cosmic ray fluxes by considering effects of the local interstellar environment on cosmic ray transport, addressing the so-called cosmic ray anisotropy problem. In particular, it is shown that the dipole amplitude and position angle below $\sim 100$ TeV are very sensitive to the velocity of the heliosphere in the local interstellar cloud and the motion of the local interstellar cloud in the local standard of rest. Better measurement of cosmic ray flux anisotropy by experiments like LHAASO and properties of the local interstellar environment by future missions like IMAP will be able to test this model.