Discovery of Gamma Rays from the Quiescent Sun with HAWC

Area of Science:

• Astrophysics
• Solar Physics
• High-Energy Astrophysics

Background:

• Previous observations with Fermi-LAT detected bright, hard GeV emission from the solar disk.
• This emission is theorized to originate from Galactic cosmic rays interacting with the solar atmosphere.
• The precise mechanisms, particularly the role of solar magnetic fields, remain unclear.

Purpose of the Study:

• To investigate the high-energy gamma-ray emission from the solar disk at TeV energies.
• To characterize the spectrum and variability of this emission.
• To test existing theoretical models of particle interactions in the solar atmosphere.

Main Methods:

• Analysis of 6.1 years of data from the High Altitude Water Cherenkov (HAWC) observatory.
• Detection of a statistically significant (6.3σ) TeV gamma-ray flux from the solar disk.
• Spectral analysis of the 0.5–2.6 TeV gamma-ray emission.

Main Results:

• First detection of a TeV gamma-ray flux from the solar disk.
• The spectrum is well-described by a power law with specific parameters (A and γ).
• A significant anticorrelation between the TeV gamma-ray flux and solar activity was observed.

Conclusions:

• The HAWC detection extends previous GeV observations to higher energies.
• The observed TeV emission likely originates from hadronic processes involving Galactic cosmic rays.
• Current models fail to fully explain the observed phenomena, highlighting the need for further theoretical development and observation.