First observations of solar halo gamma rays over a full solar cycle
We analyze 15 years of -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° 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 subdivide the data and provide the first <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>γ</a:mi> </a:math> -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 astrophysical processes near the solar surface.
Authors
- Tim Linden (ORCID: https://orcid.org/0000-0001-9888-0971)
- Isabelle John (ORCID: https://orcid.org/0000-0003-2550-7038)
- M. Crnogorčević (ORCID: https://orcid.org/0000-0002-7604-1779)
- Jung-Tsung Li (ORCID: https://orcid.org/0000-0003-1671-3171)
- J. F. Beacom (ORCID: https://orcid.org/0000-0002-0005-2631)
- Annika H. G. Peter (ORCID: https://orcid.org/0000-0002-8040-6785)
- B. Zhou (ORCID: https://orcid.org/0000-0003-1600-8835)
Institutions
- Fermi National Accelerator Laboratory (US)
- Stockholm University (SE)
- Friedrich-Alexander-Universität Erlangen-Nürnberg (DE)
- The Ohio State University at Lima (US)
- University of Chicago (US)
- Istituto Nazionale di Fisica Nucleare, Sezione di Torino (IT)
- California Consortium of Addiction Programs and Professionals (US)
- AlbaNova (SE)
- State Library of Ohio (US)
- The Ohio State University (US)
- University of Turin (IT)
Publication Details
- Journal
- Physical review. D/Physical review. D.
- Published
- 2025-11-21
- DOI
- https://doi.org/10.1103/qm68-ng62
- Primary Topic
- Solar and Space Plasma Dynamics
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- National Science Foundation
- U.S. Department of Energy
- National Aeronautics and Space Administration
- Swedish National Space Agency
- Nuclear Safety and Security Commission
- Vetenskapsrådet
- China Scholarship Council
- Office of Science
- High Energy Physics