11:00 AM - 1:00 PM
[MIS27-P04] Analysis of two Gamma-ray Glows obtained with GOOSE detector aiming at altitude measurements during the winter of FY2020 and FY2021.
Keywords:gamma-rays from lightning activity , Geometry of the electron acceleration region, Collimator detectors, Geant4
Bremsstrahlung gamma-rays due to avalanche-amplified electrons accelerated to relativistic velocity by the electrostatic field in thunderclouds are observed on the coast of the Sea of Japan in winter, and their energy can reach 30 MeV. Specifically, there are two types of gamma-rays: Terrestrial Gamma-ray Flash, which is emitted in an instant of less than 1 ms, and Gamma-ray Glow, in which the thundercloud itself emits gamma-rays for several minutes. In order to elucidate the mechanism of this acceleration, we have been conducting the GROWTH (Gamma-ray Observation of Winter Thunderclouds) experiment in the coastal areas of the Japan Sea in winter since 2006.
GOOSE detector aiming at Glow's altitude measurements, installed in Kanazawa, Ishikawa Prefecture, consists of four crystalline scintillator detectors: three collimator detectors facing straight up and tilted 30 degrees in the east-west direction, and one detector without a collimator. We analyzed the bright Glow data observed on January 9, 2021, and found that the upward-facing detectors had brighter and harder spectra, which may be evidence of relativistic beaming of bremsstrahlung. The spectrum was evaluated using Geant4 simulations that incorporate atmospheric propagation from an electron acceleration source in the sky and the detector response.
The time variability of this Glow did not show a large time difference between the east-west and the directly upward-facing collimator detectors. We simulated the time variation of the Glow with Geant4 using a model in which a compact, time-invariant accelerating source is swept by the wind, and the time difference between the east-west collimator detectors should be clearly visible. When the acceleration source was at its closest, the count rate of the top collimator should be 7-8 times higher than that of the east-west collimator, but the observation was only 2 times higher. Although it is not possible to discuss the detailed geometry from the obtained data alone, it was strongly suggested that the acceleration source is spatially extended. In this talk, I will briefly discuss how far the spatial extent of the acceleration region can be limited using the data from the January 9, 2021 Glow, and discuss the direction of future instrument development and deployment. In addition, the data analysis for the winter of 2021, including the lightning Gamma-ray Glow observed on February 16, 2022, will be presented.
GOOSE detector aiming at Glow's altitude measurements, installed in Kanazawa, Ishikawa Prefecture, consists of four crystalline scintillator detectors: three collimator detectors facing straight up and tilted 30 degrees in the east-west direction, and one detector without a collimator. We analyzed the bright Glow data observed on January 9, 2021, and found that the upward-facing detectors had brighter and harder spectra, which may be evidence of relativistic beaming of bremsstrahlung. The spectrum was evaluated using Geant4 simulations that incorporate atmospheric propagation from an electron acceleration source in the sky and the detector response.
The time variability of this Glow did not show a large time difference between the east-west and the directly upward-facing collimator detectors. We simulated the time variation of the Glow with Geant4 using a model in which a compact, time-invariant accelerating source is swept by the wind, and the time difference between the east-west collimator detectors should be clearly visible. When the acceleration source was at its closest, the count rate of the top collimator should be 7-8 times higher than that of the east-west collimator, but the observation was only 2 times higher. Although it is not possible to discuss the detailed geometry from the obtained data alone, it was strongly suggested that the acceleration source is spatially extended. In this talk, I will briefly discuss how far the spatial extent of the acceleration region can be limited using the data from the January 9, 2021 Glow, and discuss the direction of future instrument development and deployment. In addition, the data analysis for the winter of 2021, including the lightning Gamma-ray Glow observed on February 16, 2022, will be presented.