First Observations of Solar Halo Gamma Rays Over a Full Solar Cycle
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arXiv
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2025
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| author | Linden, Tim Li, Jung-Tsung Zhou, Bei John, Isabelle Crnogorčević, Milena Peter, Annika H. G. Beacom, John F. |
| author_facet | Linden, Tim Li, Jung-Tsung Zhou, Bei John, Isabelle Crnogorčević, Milena Peter, Annika H. G. Beacom, John F. |
| contents | We analyze 15 years of Fermi-LAT data and produce a detailed model of the Sun's inverse-Compton scattering emission (solar halo), which is powered by interactions between ambient cosmic-ray electrons and positrons with sunlight. By developing a novel analysis method to analyze moving sources, we robustly detect the solar halo at energies between 31.6 MeV and 100 GeV, and angular extensions up to 45$^\circ$ from the Sun, providing new insight into spatial regions where there are no direct measurements of the galactic cosmic-ray flux. The large statistical significance of our signal allows us to sub-divide the data and provide the first $γ$-ray probes into the time-variation and azimuthal asymmetry of the solar modulation potential, finding time-dependent changes in solar modulation both parallel and perpendicular to the ecliptic plane. Our results are consistent with (but with independent uncertainties from) local cosmic-ray measurements, unlocking new probes into both astrophysical and beyond-standard-model processes near the solar surface. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2505_04625 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | First Observations of Solar Halo Gamma Rays Over a Full Solar Cycle Linden, Tim Li, Jung-Tsung Zhou, Bei John, Isabelle Crnogorčević, Milena Peter, Annika H. G. Beacom, John F. High Energy Astrophysical Phenomena Solar and Stellar Astrophysics High Energy Physics - Phenomenology We analyze 15 years of Fermi-LAT data and produce a detailed model of the Sun's inverse-Compton scattering emission (solar halo), which is powered by interactions between ambient cosmic-ray electrons and positrons with sunlight. By developing a novel analysis method to analyze moving sources, we robustly detect the solar halo at energies between 31.6 MeV and 100 GeV, and angular extensions up to 45$^\circ$ from the Sun, providing new insight into spatial regions where there are no direct measurements of the galactic cosmic-ray flux. The large statistical significance of our signal allows us to sub-divide the data and provide the first $γ$-ray probes into the time-variation and azimuthal asymmetry of the solar modulation potential, finding time-dependent changes in solar modulation both parallel and perpendicular to the ecliptic plane. Our results are consistent with (but with independent uncertainties from) local cosmic-ray measurements, unlocking new probes into both astrophysical and beyond-standard-model processes near the solar surface. |
| title | First Observations of Solar Halo Gamma Rays Over a Full Solar Cycle |
| topic | High Energy Astrophysical Phenomena Solar and Stellar Astrophysics High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2505.04625 |