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

Abstract

The observed multi-GeV gamma-ray emission from the solar disk --- sourced by hadronic cosmic rays interacting with gas, and affected by complex magnetic fields --- is not understood. Utilizing an improved analysis of the Fermi-LAT data that includes the first resolved imaging of the disk, we find strong evidence that this emission is produced by two separate mechanisms. Between 2010-2017 (the rise to and fall from solar maximum), the gamma-ray emission is dominated by a polar component. Between 2008-2009 (solar minimum) this component remains present, but the total emission is instead dominated by a new equatorial component with a brighter flux and harder spectrum. Most strikingly, although 6 gamma rays above 100 GeV are observed during the 1.4 years of solar minimum, none are observed during the next 7.8 years. These features, along with a 30-50 GeV spectral dip which will be discussed in a companion paper, were not anticipated by theory. To understand the underlying physics, Fermi and HAWC observations of the imminent Cycle 25 solar minimum are crucial.

5 pages, 2 figures. Supplemental Material includes an additional 10 pages, 8 figures. To Be Submitted to Physical Review Letters

References in corpus (14)

• Propagation of an Earth-directed coronal mass ejection in three dimensions
• Fermi-LAT Observations of Two Gamma-Ray Emission Components from the Quiescent Sun
• Powerful Solar Signatures of Long-Lived Dark Mediators
• Gamma-ray emission from the solar halo and disk: a study with EGRET data
• Predicting the Amplitude and Hemispheric Asymmetry of Solar Cycle 25 with Surface Flux Transport
• Fermi-LAT Observations of High-energy Behind-the-limb Solar Flares
• Solar Atmospheric Neutrinos: A New Neutrino Floor for Dark Matter Searches
• First detection of >100 MeV gamma rays associated with a behind-the-limb solar flare
• Enhanced neutrino signals from dark matter annihilation in the Sun via metastable mediators
• Gamma-rays from halos around stars and the Sun
• Neutrinos from cosmic ray interactions in the Sun
• Solar Atmospheric Neutrinos and the Sensitivity Floor for Solar Dark Matter Annihilation Searches
• TeV Solar Gamma Rays From Cosmic-Ray Interactions
• The Kinematics and Morphology of Solar Coronal Mass Ejections

Cited by in corpus (29)

• The First Fermi-LAT Solar Flare Catalog
• Constraints on Spin-Dependent Dark Matter Scattering with Long-Lived Mediators from TeV Observations of the Sun with HAWC
• The Southern Wide-Field Gamma-Ray Observatory (SWGO): A Next-Generation Ground-Based Survey Instrument for VHE Gamma-Ray Astronomy
• First HAWC Observations of the Sun Constrain Steady TeV Gamma-Ray Emission
• The TeV Sun Rises: Discovery of Gamma rays from the Quiescent Sun with HAWC
• The Sun at GeV--TeV Energies: A New Laboratory for Astroparticle Physics
• Gamma-ray emission from the Sagittarius Dwarf Spheroidal galaxy due to millisecond pulsars
• Galactic Cosmic-Ray Propagation in the Inner Heliosphere: Improved Force-Field Model
• StellarICS: Inverse Compton Emission from the Quiet Sun and Stars from keV to TeV
• The Sun at TeV energies: gammas, neutrons, neutrinos and a cosmic ray shadow
• Searches for neutrinos from cosmic-ray interactions in the Sun using seven years of IceCube data
• The solar disk at high energies
• A New Component from the Quiet Sun: Synchrotron Radiation from Galactic Cosmic-Ray Electrons
• Extension of the synchrotron radiation of electrons to very high energies in clumpy environments
• Search for gamma-ray emission from the Sun during solar minimum with the ARGO-YBJ experiment
• Yet Another Sunshine Mystery: Unexpected Asymmetry in GeV Emission from the Solar Disk
• Small-Scale Magnetic Fields are Critical to Shaping Solar Gamma-Ray Emission
• Possible detection of gamma rays from Epsilon Eridani
• A study of super-luminous stars with the Fermi Large Area Telescope
• Role of magnetic arcades in explaining the puzzle of the gamma-ray emission from the solar disk
• Anisotropic Photon and Electron Scattering without Ultrarelativistic Approximation
• Simulating gamma-ray production from cosmic rays interacting with the solar atmosphere in the presence of coronal magnetic fields
• Puzzling Variation of Gamma Rays from the Sun over the Solar Cycle Revealed with Fermi-LAT
• The influence of the Sun and Moon on the observation of very high energy gamma-ray sources using EAS arrays
• Angular Distribution of Gamma Rays Produced in Proton-Proton Collisions
• First Observations of Solar Halo Gamma Rays Over a Full Solar Cycle
• Simulation of the isotropic ultra-high energy photons flux in the solar magnetic field and a comparison with observations made by the HAWC and Fermi-LAT observatories
• Mysterious High Energy Gamma Rays Might Help Explain What Drives Solar Cycles
• A blind search for intraday gamma-ray transients with Fermi-LAT: Detections of GRB and solar emissions