Temporal Structures in Positron Spectra and Charge-Sign Effects in Galactic Cosmic Rays

Phys. Rev. Lett. 131, 151002 (2023)
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We present the precision measurements of 11 years of daily cosmic positron fluxes in the rigidity range from 1.00 to 41.9 GV based on $3.4 \times 10^6$ positrons collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The positron fluxes show distinctly different time variations from the electron fluxes at short and long timescales. A hysteresis between the electron fluxes and the positron fluxes is observed with a significance greater than 5σat rigidities below 8.5 GV. On the contrary, the positron fluxes and the proton fluxes show similar time variation. Remarkably, we found that positron fluxes are modulated more than proton fluxes with a significance greater than 5σ for rigidities below 7 GV. These continuous daily positron fluxes, together with AMS daily electron, proton, and helium fluxes over an 11-year solar cycle, provide unique input to the understanding of both the charge-sign and mass dependencies of cosmic rays in the heliosphere.

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In the following tables we present the daily positron flux $\Phi_{e^+}$ as a function of rigidity at the top of AMS. The fluxes are in units of $[m^2 \cdot sr \cdot s \cdot \mathrm{GV}]^{−1}$ . The errors include statistics ($\sigma_\mathrm{stat.}$), time-dependent systematic errors ($\sigma_\mathrm{time}$) and the total systematic error ($\sigma_\mathrm{syst.}$). Contributions to the time-dependent systematic errors ($\sigma_\mathrm{time}$) are from: the background subtraction, the trigger efficiency, the event selection efficiencies, and the unfolding. Contributions to the total systematic error ($\sigma_\mathrm{syst.}$) are from: the time-dependent systematic error, the geomagnetic cutoff, the event selection efficiencies, and the unfolding. The days are defined as UTC time 00:00:00 - 23:59:59. The daily collection time of the positron fluxes is $(1.3 - 3.2) \times10^3$ s at 1 GV, $(4.0 - 7.3) \times 10^3$ s at 2 GV, $(1.6 - 2.2) \times10^4$ s at 5 GV, $(2.9 - 3.7) \times10^4$ s at 10 GV, $(5.4 - 6.6) \times 10^4$ s at 20 GV, and, above 30 GV, reaches $(6.0 - 7.2) \times 10^4$ s.

External Databases
AMS Data at CRDB (Cosmic-ray DataBase)

The CRDB at LPSC/IN2P3/CNRS, online since 2013, is fully described in Maurin et al. (2014, 2020)

AMS Data at Cosmic Ray DataBase (CRDB) © SSDC

The CRDB © SSDC is developed at the Space Science Data Center, a facility of the Italian Space Agency (ASI).