Terrestrial gamma-ray flashes (TGFs) were first reported using data from the Burst and Transient Source Experiment (BATSE) onboard NASA's Compton Gamma-Ray Observatory (CGRO) in 1994.
The short duration (0.2 to 3.5 milliseconds) atmospheric bursts were initially thought to be caused by relativistic runaway electron avalanches acting on natural background radiation, or extensive cosmic-ray air showers - these theories are now discounted.
Current theories include relativistic feedback or runaway electron production in the strong electric fields associated with lightning leaders or streamers, similar to the energetic radiation observed on the ground from lightning.
See :Journal of Physical Research 2008
Also see :
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