Observation of Fine Time Structures in the Cosmic Proton and Helium Fluxes with the Alpha Magnetic Spectrometer on the International Space Station

Abstract

We present the precision measurement from May 2011 to May 2017 (79 Bartels rotations) of the proton fluxes at rigidities from 1 to 60 GV and the helium fluxes from 1.9 to 60 GV based on a total of 1×10^{9} events collected with the Alpha Magnetic Spectrometer aboard the International Space Station. This measurement is in solar cycle 24, which has the solar maximum in April 2014. We observed that, below 40 GV, the proton flux and the helium flux show nearly identical fine structures in both time and relative amplitude. The amplitudes of the flux structures decrease with increasing rigidity and vanish above 40 GV. The amplitudes of the structures are reduced during the time period, which started one year after solar maximum, when the proton and helium fluxes steadily increase. Above ∼3 GV the p/He flux ratio is time independent. We observed that below ∼3 GV the ratio has a long-term decrease coinciding with the period during which the fluxes start to rise.

Updated Neutron‐Monitor Yield Function: Bridging Between In Situ and Ground‐Based Cosmic Ray Measurements

“…Considering the altitude effect as a simple barometric correction is not appropriate, especially if the correction is comparable to or exceeds one attenuation length (Flückiger et al, 2008). NMs and the CR spectra directly recorded in space by the Alpha Magnetic Spectrometer AMS-02 experiment (Aguilar et al, 2018). We also verify the stability of all NMs operating during the period of 2011-2017 covered by the AMS-02 data.…”

“…Here we update the YF by Mishev et al () and expand it to higher altitudes, from sea level up to 500 g/cm of the residual atmospheric depth (or 5.7 km altitude) and validate it using data from different NMs and the CR spectra directly recorded in space by the Alpha Magnetic Spectrometer AMS‐02 experiment (Aguilar et al, ). We also verify the stability of all NMs operating during the period of 2011–2017 covered by the AMS‐02 data.…”

“…As the input spectra ( in equation ) we used spectra of protons and helium measured by AMS‐02 experiment (Aguilar et al, ) for the period May 2011 through May 2017. The spectra were measured for 79 Bartels rotations (BR) 27 days each, 2,426–2,506.…”

Cosmic-ray interactions with the Sun using the fluka code

“…[51]. We also use the AMS-02 spectra measured for different Bartels' rotations (BRs) [52,53]. 5 Since the AMS-02 spectra are available starting from about 0.4 GeV/n, we have extrapolated the data down to 0.1 GeV/n by fitting the measured intensities with a function given by [54]: 4 We use the total intensity of electrons and positrons, and we refer to them as electrons.…”

“…[4,56]. In addition, the AMS-02 detector on the International Space Station started its operations only in May 2011 and, at present, their data are available until May 2017 [52,53]. Therefore, with the simulation set-up that we have implemented for this work, we are not able to make predictions on the gamma-ray flux in the period corresponding to the analysis of Ref.…”