A new population of Terrestrial Gamma-ray Flashes

Terrestrial Gamma-ray Flashes (TGFs) consist of large numbers of highenergy photons produced in thunderstorms in connection with the lightning flash, and are the most energetic photon phenomenon naturally occurring on Earth. The satellite RHESSI, originally designed for observing solar flares, is also able to register gamma-rays from Earth. Algorithms for finding TGFs in the RHESSI data have been purposefully conservative, but Østgaard et al. [2015] presented a method to identify TGFs that were not part of previous RHESSI TGF catalogs. By superposing RHESSI data intervals for each lightning detection by the World Wide Lightning Location Network (WWLLN) within RHESSI’s field-of-view, they showed that there exists a group of weak signal TGFs. Expanding on this work we here provide a statistical analysis comparing the signal strength to both background levels and to a Poisson distribution. We seek to optimize the range of the search parameters in order to minimize the chance of including background events. The geographical distribution of the TGFs will also be investigated. As many of the TGFs we work with have a weak signal, they can be difficult to distinguish from the background level. Because of this the factors that cause variation of the incoming background radiation levels are of interest to us, and we have identify several such factors.Masteroppgave i fysikkMAMN-PHYSPHYS39