AGILE Observations of Terrestrial Gamma-Ray Flashes

The AGILE satellite, operating since mid 2007 and primarily devoted to high-energy astrophysics,is one of the only three currently operating space instruments capable of detecting TerrestrialGamma-Ray Flashes (TGFs), together with RHESSI and Fermi-GBM. Thanks to the AGILEMini-Calorimeter instrument energy range extended up to 100MeV and its flexible trigger logic onsub-millisecond time scales, AGILE is detecting more than 10 TGFs/month, adding a wealth ofobservations which pose severe constrains on production models. The main AGILE discoveries inTGF science during two and a half years of observations are the following: 1) the TGF spectrumextends well above 40 MeV, 2) the high energy tail of the TGF spectrum is harder than expectedand cannot be easily explained by previous theoretical models, 3) TGFs can be localized from spaceusing high-energy photons detected by the AGILE gamma-ray imaging detector. In this presenta-tion we will describe the characteristics of the 2.5-years AGILE TGF sample, focusing on the recentresults concerning the TGF high-energy spectral characteristics.I. INTRODUCTION