Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica
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| Main Authors: | , , , , , , , , , |
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| Format: | Preprint |
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2024
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| _version_ | 1866910576258580480 |
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| author | Muangha, Pradiphat Ruffolo, David Sáiz, Alejandro Banglieng, Chanoknan Evenson, Paul Seunarine, Surujhdeo Oh, Suyeon Jung, Jongil Duldig, Marc Humble, John |
| author_facet | Muangha, Pradiphat Ruffolo, David Sáiz, Alejandro Banglieng, Chanoknan Evenson, Paul Seunarine, Surujhdeo Oh, Suyeon Jung, Jongil Duldig, Marc Humble, John |
| contents | 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 rotation, especially near sunspot minimum, while the flux occasionally exhibited a strong harmonic at 13.5 days, and that the magnetic field component along a nominal Parker spiral (i.e., the magnetic sector structure) is a strong determinant of such spectral and flux variations, with the solar wind speed exerting an additional, nearly rigidity-independent influence on flux variations. Our investigation affirms the capability of ground-based NM stations to accurately and continuously monitor cosmic ray spectral variations in the long-term future. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2408_13999 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica Muangha, Pradiphat Ruffolo, David Sáiz, Alejandro Banglieng, Chanoknan Evenson, Paul Seunarine, Surujhdeo Oh, Suyeon Jung, Jongil Duldig, Marc Humble, John High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics 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 rotation, especially near sunspot minimum, while the flux occasionally exhibited a strong harmonic at 13.5 days, and that the magnetic field component along a nominal Parker spiral (i.e., the magnetic sector structure) is a strong determinant of such spectral and flux variations, with the solar wind speed exerting an additional, nearly rigidity-independent influence on flux variations. Our investigation affirms the capability of ground-based NM stations to accurately and continuously monitor cosmic ray spectral variations in the long-term future. |
| title | Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica |
| topic | High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2408.13999 |