Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica ...

• Main Authors: Muangha, Pradiphat, Ruffolo, David, Sáiz, Alejandro, Banglieng, Chanoknan, Evenson, Paul, Seunarine, Surujhdeo, Oh, Suyeon, Jung, Jongil, Duldig, Marc, Humble, John
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: arXiv 2024
• Subjects: High Energy Astrophysical Phenomena astro-ph.HE; Instrumentation and Methods for Astrophysics astro-ph.IM; FOS: Physical sciences; Antarc*; Antarctic; Antarctica; South pole
• Online Access: https://dx.doi.org/10.48550/arxiv.2408.13999; https://arxiv.org/abs/2408.13999

A technique has recently been developed for tracking short-term spectral variations in Galactic cosmic rays (GCRs) using data from a single neutron monitor (NM), by collecting histograms of the time delay between successive neutron counts and extracting the leader fraction $L$ as a proxy of the spectral index. Here we analyze $L$ from four Antarctic NMs during 2015 March to 2023 September. We have calibrated $L$ from the South Pole NM with respect to a daily spectral index determined from published data of GCR proton fluxes during 2015--2019 from the Alpha Magnetic Spectrometer (AMS-02) aboard the International Space Station. Our results demonstrate a robust correlation between the leader fraction and the spectral index fit over the rigidity range 2.97--16.6 GV for AMS-02 data, with uncertainty 0.018 in the daily spectral index as inferred from $L$. In addition to the 11-year solar activity cycle, a wavelet analysis confirms a 27-day periodicity in the GCR flux and spectral index corresponding to solar ... : 17 pages, 10 figures ...