Speaker
Description
Thunderclouds are known to emit minute-long gamma-ray bursts, commonly referred to as gamma-ray glows. These emissions are believed to originate from bremsstrahlung produced by high-energy electrons accelerated within the clouds. We conducted winter lightning observations in a mountainous area of Niigata, Japan, where thunderclouds are easily observable. Our detection system comprises various scintillation detectors, including BGO, CsI(Tl), SrI2(Eu), and a high-purity germanium (HPGe) detector, to search for line gamma-ray emissions such as nuclear gamma rays and pair annihilation lines (511 keV). On December 24, 2024, we observed a gamma-ray glow event lasting approximately three minutes. Radar data indicated the presence of rain clouds over the observation site during this period. Each detector recorded an increase in gamma-ray count rates. In addition to the enhancement of continuum emissions, we detected tentative line emissions between 200 and 600 keV. Although the event was relatively weak as a gamma-ray glow, the presence of line-like features suggests that future, more intense events may reveal clearer spectral structures.
