A ground level gamma-ray burst observed in association with rocket-triggered lightning

We report the observation of an intense gamma-ray burst observed on the ground at sea level, produced in association with the initial-stage of rocket-triggered lightning at the International Center for Lightning Research and Testing at Camp Blanding, FL. The burst was observed simultaneously on three NaI(Tl)/photomultiplier tube detectors that were located 650 m from the triggered lightning channel with gamma-ray energies extending up to more than 10 MeV. The burst consisted of 227 individual gamma-rays that arrived over a 300 ms time period in coincidence with an 11 kA current pulse. The burst of gamma-rays had very different characteristics from the x-ray emission frequently seen in association with the dart leader/return stroke sequences of triggered lightning and may represent a new kind of event, likely originating from cloud processes thousands of meters overhead.