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Charge-Sign Dependent Cosmic-Ray Modulation Observed with the Calorimetric Electron Telescope on the International
O Adriani1,2, Y Akaike3,4, K Asano5
1Department of Physics, University of Florence, Via Sansone, 1 - 50019, Sesto Fiorentino, Italy.
Physical Review Letters
|June 9, 2023
Summary
Galactic cosmic rays (GCRs) show charge-sign dependent solar modulation, with electrons varying more than protons. This finding, observed over six years, confirms the drift effect in heliospheric transport models.
Area of Science:
- * Space Physics
- * Astroparticle Physics
Background:
- * Galactic cosmic rays (GCRs) are high-energy particles originating from outside the solar system.
- * Solar modulation describes how the solar magnetic field and solar wind affect GCRs reaching Earth.
- * Previous studies indicated charge-sign dependent effects, but direct observation with a single detector was limited.
Purpose of the Study:
- * To investigate the charge-sign dependent solar modulation of GCRs.
- * To validate GCR count rate measurements using neutron monitor data.
- * To compare the modulation amplitudes of GCR electrons and protons at similar rigidities.
Main Methods:
- * Utilized data from the Calorimetric Electron Telescope (CALET) on the International Space Station (ISS).
- * Analyzed six years of GCR electron and proton count rates during a positive solar magnetic field polarity period.
- * Employed a numerical drift model to simulate GCR transport in the heliosphere.
Main Results:
- * Observed a clear charge-sign dependent solar modulation of GCRs.
- * Proton count rate variations were consistent with neutron monitor data.
- * Both electron and proton count rates showed anticorrelation with the heliospheric current sheet tilt angle.
- * Electron count rate variations were significantly larger than proton count rate variations.
Conclusions:
- * The observed charge-sign dependence is a direct signature of the drift effect in GCR transport.
- * The drift model successfully reproduces the observed charge-sign dependent modulation.
- * CALET's observations provide strong evidence for charge-dependent drift mechanisms influencing GCRs.
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