Hard, Bright X‐Ray Bursts in Natural Lightning: Blurring the Boundary Between X‐Ray Bursts and TGFs

Abstract In this study, we analyzed a rare hard, bright X‐ray burst associated with intense natural lightning. Through spectral analysis and source model fitting, we demonstrate that the energy spectrum of the X‐ray source region exhibits significant uncertainty due to the strong dependence on radiation beam geometry, which may appear as a TGF‐like hard spectrum. The X‐ray burst is estimated to produce approximately 10 13 to 10 14 source photons (>30 keV), which is 1–2 orders of magnitude higher than a typical X‐ray burst and comparable to the brightness of downward TGFs. The hard, bright X‐ray burst challenges the traditional classification boundary between soft/weak X‐rays and hard/strong TGFs, suggesting that both may exist in a continuous spectrum. The generation mechanism for such hard, bright X‐ray bursts may involve Relativistic Runaway Electron Avalanche processes, though likely in an incomplete stage.