Simulating gamma-ray production from cosmic rays interacting with the solar atmosphere in the presence of coronal magnetic fields

Cosmic rays can interact with the solar atmosphere and produce a slew of secondary messengers,making the Sun a bright gamma-ray source in the sky.Detailed observations with Fermi-LAT have shown that these interactions must be strongly affected by solar magnetic fields in order to produce a wide range of observational features,such as a high flux and hard spectrum.However,the detailed mechanisms behind these features are still a mystery.In this study,we tackle this problem by performing particle-interaction simulations in the solar atmosphere in the presence of coronal magnetic fields using the potential field source surface(PFSS)model.We find that low-energy(~GeV)gamma-ray production is significantly enhanced by the coronal magnetic fields,but the enhancement decreases rapidly with energy.The enhancement directly correlates with the production of gamma rays with large deviation angles relative to the input cosmic-ray direction.We conclude that coronal magnetic fields are essential for correctly modeling solar disk gamma rays below 10 GeV,but above that,the effect of coronal magnetic fields diminishes.Other magnetic field structures are needed to explain the high-energy disk emission.

Monitoring the daily variation of Sun-Earth magnetic fields using galactic cosmic rays

The interplanetary magnetic field(IMF)between the Sun and Earth is an extension of the solar magnetic field carried by the solar wind into interplanetary space.Monitoring variations in the IMF upstream of the Earth would provide very important information for the prediction of space weather effects,such as effects of solar storms and the solar wind,on human activity.In this study,the IMF between the Sun and Earth was measured daily for the first time using a cosmicray observatory.Cosmic rays mainly consist of charged particles that are deflected as they pass through a magnetic field.