Evidence for a New Component of High-Energy Solar Gamma-Ray Production.

Area of Science:

• * Astrophysics
• * Solar Physics
• * High-Energy Astrophysics

Background:

• * Multi-GeV gamma-ray emission from the solar disk is observed but not well understood.
• * The emission is thought to originate from hadronic cosmic rays interacting with solar gas and magnetic fields.
• * Previous analyses lacked detailed imaging of the solar disk.

Purpose of the Study:

• * To investigate the origin and mechanisms of solar disk gamma-ray emission.
• * To analyze Fermi-LAT data with improved imaging capabilities.
• * To understand the variability of gamma-ray emission across the solar cycle.

Main Methods:

• * Utilized an improved analysis of Fermi-LAT data, incorporating resolved imaging of the solar disk.
• * Differentiated gamma-ray emission components based on solar cycle phase (minimum vs. maximum).
• * Analyzed the spectral properties and flux of gamma-ray emissions.

Main Results:

• * Evidence found for two distinct gamma-ray emission mechanisms: a polar component and a new equatorial component.
• * The equatorial component dominated during solar minimum (2008-2009) with brighter flux and harder spectrum.
• * A striking absence of >100 GeV gamma rays was observed during the subsequent 7.8 years (solar maximum) compared to solar minimum.

Conclusions:

• * The observed features, including a spectral dip, were not predicted by current theories.
• * Future Fermi-LAT and HAWC observations during the upcoming solar cycle 25 minimum are crucial for understanding the underlying physics.
• * The study highlights the need for revised theoretical models to explain solar gamma-ray emission.