Compton Scattering Effects on the Spectral and Temporal Properties of Terrestrial Gamma-Ray Flashes

Abstract : Terrestrial gamma-ray flashes (TGFs) are high-energy photon bursts originating from the Earth's atmosphere. In this study, using first-principles Monte Carlo simulations, we quantify the effects of Compton scattering on the temporal and spectral properties of TGFs induced by a tilted source geometry. Modeling results indicate that the source orientation is a critical parameter in TGF analysis but has been significantly underestimated in previous studies. Offset distance between the lightning source and satellite location cannot be used as a single parameter characterizing Compton scattering effects. In the tilted geometry, Compton scattering effects are more pronounced in the falling part of TGF pulses and can lead to an increase of the falling part of TGF pulses by several tens of microseconds. Moreover, by performing curve-fitting analysis on simulated TGF light curves, we explain how the symmetric and asymmetric pulses measured by the Gamma-Ray Burst Monitor on Fermi satellite are consistent with the Compton scattering effects. Fermi-measured TGF pulses can be fully explained using Gaussian-distributed TGF sources with an average duration of ∼206 μs.