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○ 일시: 10월 11일(화) 오후 3:00
○ 장소: 기초과학연구소 세미나실 (제1과학관 3층 31317호)
○ 연사: Dr. Bagrat Mailyan (University of Alabama, USA)
○ Title: Analysis of Individual Terrestrial Gamma-ray Flashes
○ Abstract:
We report
on the spectral analysis of individual Terrestrial Gamma-ray Flashes (TGFs)
observed with the Fermi Gamma-ray Burst Monitor (GBM).
The large GBM TGF sample provides 46 events suitable for individual spectral
analysis: sufficiently bright, localized by ground-based radio, and with
the gamma rays reaching a detector unobstructed. These TGFs exhibit diverse
spectral characteristics that are hidden when using summed analysis methods. We
account for the low counts in individual TGFs by using Poisson likelihood, and
we also consider instrumental effects.
The data are fit with models obtained from Monte Carlo simulations of the large
scale Relativistic Runaway Electron Avalanche (RREA) model, including
propagation through the atmosphere. Source altitudes ranging from 11.6 to
20.2 km are simulated. Two beaming geometries were considered: In one, the
photons retain the intrinsic distribution from scattering (narrow), and in
the other, the photons are smeared into a wider beam (wide).
Several TGFs are well fit only by narrow models, while others favor wide
models. Large-scale RREA models can accommodate both narrow and wide
beams, with narrow beams suggest large-scale RREA in organized electric
fields while wide beams may imply converging or diverging electric
fields.
Wide beams are also consistent with acceleration in the electric fields of
lightning leaders, but the TGFs that favor narrow beam models appear
inconsistent with some lightning leader models.