SoftwareDetermining a lower limit of luminosity for the first satellite observation of a reverse beam terrestrial gamma-ray flash associated with a cloud to ground lightning leaderChaffin, Jeffrey; Pu, Yunjiao; Smith, David; Cummer, Steve; Splitt, Mike{"Abstract":["We provide an updated analysis of the gamma-ray signature of a terrestrial gamma ray flash (TGF) detected by the Fermi Gamma-ray Burst Monitor first reported by Pu et al. 2020. A TGF produced 3 ms prior to a negative cloud-to-ground return stroke was close to simultaneous with an isolated low frequency radio pulse during the leader&#39;s propagation, with a polarity indicating downward moving negative charge. In prior observations this &#39;slow&#39; low frequency signal has been strongly correlated with upward (opposite polarity) directed TGF events [Pu et al. 2019; Cummer et al. 2011] leading the authors to conclude that the Fermi gamma ray observation is actually the result of a reverse positron beam generating upward directed gamma rays. We investigate the feasibility of this scenario and determine a lower limit on the luminosity of the downward TGF from the perspective of gamma-ray timing uncertainties, TGF Monte Carlo simulations, and meteorological analysis of a model storm cell and its possible charge structure altitudes. We determined the most likely source altitude of the reverse beam TGF to be 7.5 km &#43;/- 2.6 km, just below an estimated negative charge center at 8 km. At that altitude the Monte Carlo simulations indicate a lower luminosity limit of 2 x 10^18 photons above 1 MeV for the main downward beam of the TGF making the reverse beam detectable by the Fermi Gamma Ray Burst Monitor."],"Other":["Geant4 Python Funding provided by: National Science Foundation<br />Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001<br />Award Number: AGS-193598"]}Zenodo2023-03-1510661856https://doi.org/10.5281/zenodo.77306742235299nullMIT LicenseNational Science Foundation