How well do we understand charged particle propagation in the solar system? This is an important topic for both astrophysics and space weather. Unfortunately, we still lack a fully predictive theory to this problem; a major challenge to this is the lack of cosmic-ray (CR) measurement throughout the solar system, as most data are measured locally on Earth.
I propose to overcome this hurdle in my SolarIC project by using the solar inverse-Compton (IC) emission—produced by CR electrons scattering with Sunlight—as a remote probe for CR distribution throughout the solar system. I will achieve this through three main results. First, I will detect and analyze the solar IC emission with Fermi-LAT data to study its morphology and time dependence. Second, I will calculate the theoretical prediction of the solar IC emission for both GeV and MeV regimes, utilizing state-of-the-art CR simulations. This will be a theoretical foundation for interpreting the data. And for the first time, I will compute the polarization signatures of solar IC emission. Third, building on the previous two results, I will constrain and test contemporary models of CR propagation in the solar system through cross correlation of the Fermi-LAT data with the theory prediction. I will also perform a mock tomographic analysis of the solar IC emission, utilizing the polarization signature. This will be an important and novel prediction for the proposed future MeV space gamma-ray telescopes, such as e-ASTROGAM.
Through my SolarIC project, I will demonstrate that solar IC emission can be used to provide valuable data and constraints on CR distribution in the solar system. This will be an important step leading to a better understanding of charged-particle propagation in the solar system, which will have significant impacts on many astrophysics disciplines including solar physics, cosmic-ray physics, neutrino astrophysics, and dark matter searches.