Sun reveals hidden gamma-ray source in powerful solar flares

NJIT researchers traced gamma rays from a September 10, 2017 X8.2 solar flare to a compact region in the corona and identified a previously unknown, very high-energy particle population linked to bremsstrahlung emission.

Researchers at the New Jersey Institute of Technology have identified where and how intense gamma rays are produced during a major solar flare, addressing a long-standing question in solar physics. The team analysed an X8.2-class flare from September 10, 2017, combining gamma-ray observations from NASA's Fermi Space Telescope with microwave imaging from NJIT's Expanded Owens Valley Solar Array. Their work links the gamma rays to a compact region in the solar corona and to a specific radiative process. The discovery was reported in Nature Astronomy and refines understanding of particle acceleration in large flares. Key findings: - The analysis combined Fermi gamma-ray data with microwave imaging from NJIT's Expanded Owens Valley Solar Array to study the X8.2 flare on September 10, 2017. - The result, published in Nature Astronomy, identifies a compact coronal source responsible for the observed gamma-ray emission. - Researchers report a previously unknown class of particles accelerated to several million electron volts, moving near the speed of light and carrying far more energy than typical flare particles. - The gamma rays were traced to bremsstrahlung, where lightweight charged particles emit high-energy light when they impact material in the Sun's atmosphere. - The particle population shows an unusual energy distribution, with most particles concentrated at very high energies and relatively few at lower energies. - The high-energy region lies near places where magnetic fields decay rapidly, supporting theories that magnetic energy release drives intense acceleration; researchers say it remains unresolved whether the particles are electrons or positrons, and planned polarisation measurements with an upgraded OVSA may help answer that question. Summary: The study narrows how gamma rays arise in major solar flares and fills gaps in flare physics, which researchers report may inform space weather forecasting. Teams plan further observations using an upgraded Expanded Owens Valley Solar Array to measure microwave polarisation and test whether the energetic particles are electrons or positrons, with additional analysis ongoing to explore broader implications.