Observation of Complex Time Structures in the Cosmic-Ray Electron and Positron Fluxes with the Alpha Magnetic Spectrometer on the International Space Station

Abstract

We present high-statistics, precision measurements of the detailed time and energy dependence of the primary cosmic-ray electron flux and positron flux over 79 Bartels rotations from May 2011 to May 2017 in the energy range from 1 to 50 GeV. For the first time, the charge-sign dependent modulation during solar maximum has been investigated in detail by leptons alone. Based on $23.5 \times 10^6$ events, we report the observation of short-term structures on the timescale of months coincident in both the electron flux and the positron flux. These structures are not visible in the e+/e flux ratio. The precision measurements across the solar polarity reversal show that the ratio exhibits a smooth transition over $830 \pm 30$ days from one value to another. The midpoint of the transition shows an energy dependent delay relative to the reversal and changes by $260 \pm 30$ days from 1 to 6 GeV.

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Time-averaged (May 20, 2011 – May 11, 2017) electron flux $\Phi_{e^-}$, positron flux $\Phi_{e^+}$, and flux ratio $R_e$ as function of energy $\tilde{E}$ at the top of AMS, and their respective statistical uncertainties $\sigma_{\rm stat}$ and total systematic uncertainties $\sigma_{\rm syst}$. The total systematic uncertainties are calculated as the quadratic sum of the individual systematic uncertainties. The small differences between $\Phi_{e^+}/\Phi_{e^-}$ and $R_e$ are due to the independent optimizations of the flux and ratio analyses.

The electron flux $\Phi_{e^-}$, the positron flux $\Phi_{e^+}$, and the flux ratio $R_e$, vs energy at the top of AMS, and the respective statistical uncertainties $\sigma_{\rm stat}$ and total systematic uncertainties $\sigma_{\rm syst}$. Days from May 15 to May 19, 2011 are not included because AMS data taking started on May 20, 2011. The total systematic uncertainties are calculated as the quadratic sum of the individual systematic uncertainties. The small differences between $\Phi_{e^+}/\Phi_{e^-}$ and $R_e$ are due to the independent optimizations of the flux and ratio analyses.

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