Enhanced detection of Terrestrial Gamma-Ray Flashes by AGILE

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Martino Marisaldi1, Andrea Argan2, Alessandro Ursi3, Thomas Gjesteland4, Fabio Fuschino5, Claudio Labanti1, Marcello Galli6, Marco Tavani2, Carlotta Pittori7, Francesco Verrecchia7, Fabio D'Amico8, Nikolai Ostgaard9, Sandro Mereghetti10, Riccardo Campana1, Paolo Cattaneo11, Andrea Bulgarelli1, Sergio Colafrancesco12, Stefano Dietrich13, Francesco Longo14, Fulvio Gianotti1, Paolo Giommi7, Andrea Rappoldi11, Massimo Trifoglio1 and Alessio Trois15, (1)National Institute for Astrophysics, Bologna, Italy, (2)INAF IAPS, Roma, Italy, (3)IAPS-INAF, Rome, Italy, (4)University of Agder, Grimstad, Norway, (5)Università di Bologna, Dipartimento di Fisica e Astronomia, Bologna, Italy, (6)ENEA, Bologna, Italy, (7)ASI Science Data Center, Roma, Italy, (8)Italian Space Agency, Roma, Italy, (9)University of Bergen, Birkeland Centre for Space Science, Bergen, Norway, (10)INAF IASF Milano, Milano, Italy, (11)INFN, Pavia, Italy, (12)INAF Osservatorio Astronomico di Roma, Roma, Italy, (13)CNR ISAC, Roma, Italy, (14)Università di Trieste, Dipartimento di Fisica, Trieste, Italy, (15)INAF Osservatorio di Radioastronomia, Cagliari, Italy
At the end of March 2015 the onboard configuration of the AGILE satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter instrument. The motivation for such a change was the understanding that the dead time induced by the anticoincidence prevented the detection of a large fraction of Terrestrial Gamma-ray Flashes (TGFs), especially the short duration ones. We present here the characteristics of the new TGF sample after several months of stable operations with the new configuration. The configuration change was highly successful resulting in the detection of about 100 TGFs/month, an increase of a factor about 11 in TGFs detection rate with respect to previous configuration. As expected, the largest fraction of the new events has short duration, with a median duration of 80 microseconds. We also obtain a sample of events with simultaneous association, within 100 microseconds, with lightning sferics detected by the World Wide Lightning Location Network (WWLLN), confirming previous results reported by the Fermi mission. Given the high detection rate and the AGILE very low (+/-2.5°) orbital inclination, the new configuration provides the largest TGF detection rate surface density (TGFs / km2 / year) to date, opening space for correlation studies with lightning and atmospheric parameters on short spatial and temporal scales along the equatorial region. Eventually, the events with associated simultaneous WWLLN sferics provide a highly reliable sample to probe the long-standing issue of the TGF maximal energy.