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Marisaldi M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Argan A.,National institute for astrophysics | Trois A.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Giuliani A.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 62 more authors.
Physical Review Letters

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20a MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by the AGILE Mini-Calorimeter. We detect 8a TGFs with gamma-ray photons of energies above 20A MeV localized by the AGILE gamma-ray imager with an accuracy of ∼5-10° at 50A MeV. Remarkably, all TGF-associated gamma rays are compatible with a terrestrial production site closer to the subsatellite point than 400A km. Considering that our gamma rays reach the AGILE satellite at 540A km altitude with limited scattering or attenuation, our measurements provide the first precise direct localization of TGFs from space. © 2010 The American Physical Society. Source

It is investigated how finite regolith conductivity influences the magnitude of strong electric fields required for lofting dust grains above the surface. It is shown that even very weak conductivity typical for the lunar regolith restricts the maximum values of the local electric fields formed near mini-craters or mini-hills on the dark side of the Moon. As a result the lofting of dust grains from the surface of the Moon is suppressed significantly. The effect depends on the regolith conductivity, parameters of the solar wind plasma, and the steepness of the slopes of the mini-crater or mini-hill. © 2015 Elsevier Ltd. Source

Tavani M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Tavani M.,University of Rome Tor Vergata | Marisaldi M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Labanti C.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 70 more authors.
Physical Review Letters

Strong electric discharges associated with thunderstorms can produce terrestrial gamma-ray flashes (TGFs), i.e., intense bursts of x-rays and γ-rays lasting a few milliseconds or less. We present in this Letter new TGF timing and spectral data based on the observations of the Italian Space Agency AGILE satellite. We determine that the TGF emission above 10 MeV has a significant power-law spectral component reaching energies up to 100 MeV. These results challenge TGF theoretical models based on runaway electron acceleration. The TGF discharge electric field accelerates particles over the large distances for which maximal voltages of hundreds of megavolts can be established. The combination of huge potentials and large electric fields in TGFs can efficiently accelerate particles in large numbers, and we reconsider here the photon spectrum and the neutron production by photonuclear reactions in the atmosphere. © 2010 The American Physical Society. Source

Fuschino F.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Marisaldi M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Labanti C.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Barbiellini G.,University of Trieste | And 61 more authors.
Geophysical Research Letters

The AGILE satellite detects Terrestrial Gamma-ray Flashes (TGFs) in the 0.35-100 MeV energy range using its Mini-Calorimeter (MCAL) instrument with an average detection rate of 10 TGFs/month. Thanks to its Low Earth Orbit with only 2.5 degree of inclination, AGILE guarantees an unprecedented exposure above the equator, where both lightning activity and TGF detection peak. Here we report the comparison between the AGILE TGFs detected between March 2009 and February 2010 and full climatology lightning worldwide distribution based on satellite optical observations from LIS (Lightning Imaging Sensor) and OTD (Optical Transient Detector) instruments. This approach is complementary to the one-to-one TGF/lightning correlations by ground-based sferics measurements. Based on mono and bi-dimensional Kolmogorov-Smirnov tests, we show that the AGILE TGFs and time-averaged global lightning in the equatorial area are not drawn from the same distribution. However, we find significant regional differences in the degree of correlation as well as in the TGF/lightning ratio. In the case of south east Asia we find a 87% probability for the TGF and lightning being samples of the same distribution. This result supports the idea that the physical conditions at play in TGF generation can have strong geographical and climatological modulation. Based on the assumption that the observed range of TGF/flash ratio holds at all latitudes we can estimate a global rate of N 220 570 TGFs per day. The observed TGF/flash geographical modulation as well as the TGF global rate estimate are in agreement with previous observations. Copyright 2011 by the American Geophysical Union. Source

Matveyenko L.I.,IKI | Sivakon S.S.,IKI | Demichev V.A.,IKI | Graham D.A.,MPIfR | And 2 more authors.
Proceedings of the International Astronomical Union

Super H2O outbursts accompany star formation. We have been studying this phenomenon in Orion KL starting in 1971.8. © 2013 International Astronomical Union. Source

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