Fluence distribution of terrestrial gamma ray flashes observed by the Fermi Gamma-ray Burst Monitor

摘要

[1] The observed γ ray fluence distribution of terrestrial gamma ray flashes (TGFs) detected by the Fermi Gamma-ray Burst Monitor (GBM) is altered by instrumental effects. We perform corrections for dead time, pulse pileup, and detection efficiency in a model-independent manner. A sample of 106 GBM TGFs is selected to include both TGFs that triggered GBM and weaker TGFs found using an off-line search. Detector dead time and pulse pileup lower the observed fluence of each TGF and the detection efficiency causes weaker TGFs to have a lower probability of detection than brighter TGFs. Monte Carlo simulations are performed in each case to correct for these effects. The corrected fluence distribution is well fit with a power law of index α = –2.20 ± 0.13. This is consistent with previous estimates using other techniques. Neither a high-fluence cutoff nor a low-fluence limit is found. The fluence distribution is also expressed in units of TGF h~(–1) km~(–2) versus photons cm~(–2) per TGF.