365 research outputs found
A Joint LINET and ISS-LIS View of Lightning Distribution over the Mt. Cimone Area within the GAMMA-FLASH Program
GPM-DPR Observations on TGFs Producing Storms
Unique spaceborne measurements of the three-dimensional structure of convective
clouds producing terrestrial gamma ray flashes (TGFs) were performed using both active and passive
microwave sensors on board the Global Precipitation Measurement (GPM)-Core Observatory satellite,
finding coherent features for nine TGF-producing storms. The delineation of cloud structure using the
radar reflectivity factor shows convective cells with significant vertical development and thick layers with
high ice content. Compared to other cumulonimbus clouds in the tropics, the TGFs counterparts have
higher reflectivity values above 3 and 8 km altitude showing in all cases a cumulonimbus tower and the
TGFs locations are very close, or coincident, to these high Z columns, where reflectivity exceeds 50dBz.
Using the GPM Microwave Imager radiometer, most thunderstorms show a very strong depression of
polarization corrected temperature (PCT) at channel 89GHz, indicating a strong scattering signal by ice
in the upper cloud layers. At channel 166GHZ, the difference between vertical and horizontal brightness
temperature signal always returns positive values, from 0.2 up to 13.7K indicating a complex structure
with randomly/vertically oriented ice particles. The PCT was used to characterize the analyzed storms
in terms of hydrometeor types, confirming in 7/9 cases a high likelihood of hail/graupel presence. To
perform analysis on the TGFs parent flashes, radio atmospherics data from the Earth Networks Total
Lightning Network lightning network were used. Waveform data indicate that all cases are intra-cloud
events and TGFs typically take place during the peak of flash rate production. Finally, the analysis of the
most intense event is shown
The X-Gamma Imaging Spectrometer (XGIS) onboard THESEUS
A compact and modular X and gamma-ray imaging spectrometer (XGIS) has been
designed as one of the instruments foreseen on-board the THESEUS mission
proposed in response to the ESA M5 call. The experiment envisages the use of
CsI scintillator bars read out at both ends by single-cell 25 mm 2 Silicon
Drift Detectors. Events absorbed in the Silicon layer (lower energy X rays) and
events absorbed in the scintillator crystal (higher energy X rays and
Gamma-rays) are discriminated using the on-board electronics. A coded mask
provides imaging capabilities at low energies, thus allowing a compact and
sensitive instrument in a wide energy band (~2 keV up to ~20 MeV). The
instrument design, expected performance and the characterization performed on a
series of laboratory prototypes are discussed.Comment: To be published in the Proceedings of the THESEUS Workshop 2017
(http://www.isdc.unige.ch/theseus/workshop2017.html), Journal of the Italian
Astronomical Society (Mem.SAIt), Editors L. Amati, E. Bozzo, M. Della Valle,
D. Gotz, P. O'Brien. Details on the THESEUS mission concept can be found in
the white paper Amati et al. 2017 (arXiv:171004638) and Stratta et al. 2017
(arXiv:1712.08153
GAME: Grb and All-sky Monitor Experiment
We describe the GRB and All-sky Monitor Experiment (GAME) mission submitted
by a large international collaboration (Italy, Germany, Czech Repubblic,
Slovenia, Brazil) in response to the 2012 ESA call for a small mission
opportunity for a launch in 2017 and presently under further investigation for
subsequent opportunities. The general scientific objective is to perform
measurements of key importance for GRB science and to provide the wide
astrophysical community of an advanced X-ray all-sky monitoring system. The
proposed payload was based on silicon drift detectors (~1-50 keV), CdZnTe (CZT)
detectors (~15-200 keV) and crystal scintillators in phoswich (NaI/CsI)
configuration (~20 keV-20 MeV), three well established technologies, for a
total weight of ~250 kg and a required power of ~240 W. Such instrumentation
allows a unique, unprecedented and very powerful combination of large field of
view (3-4 sr), a broad energy energy band extending from ~1 keV up to ~20 MeV,
an energy resolution as good as ~300 eV in the 1-30 keV energy range, a source
location accuracy of ~1 arcmin. The mission profile included a launch (e.g., by
Vega) into a low Earth orbit, a baseline sky scanning mode plus pointed
observations of regions of particular interest, data transmission to ground via
X-band (4.8 Gb/orbit, Alcantara and Malindi ground stations), and prompt
transmission of GRB / transient triggers.Comment: 13 pages, 8 figures, published in International Journal of Modern
Physics
AGILE detection of delayed gamma-ray emission from GRB 080514B
GRB 080514B is the first gamma ray burst (GRB), since the time of EGRET, for
which individual photons of energy above several tens of MeV have been detected
with a pair-conversion tracker telescope. This burst was discovered with the
Italian AGILE gamma-ray satellite. The GRB was localized with a cooperation by
AGILE and the interplanetary network (IPN). The gamma-ray imager (GRID)
estimate of the position, obtained before the SuperAGILE-IPN localization, is
found to be consistent with the burst position. The hard X-ray emission
observed by SuperAGILE lasted about 7 s, while there is evidence that the
emission above 30 MeV extends for a longer duration (at least ~13 s). Similar
behavior was seen in the past from a few other GRBs observed with EGRET.
However, the latter measurements were affected, during the brightest phases, by
instrumental dead time effects, resulting in only lower limits to the burst
intensity. Thanks to the small dead time of the AGILE/GRID we could assess that
in the case of GRB 080514B the gamma-ray to X-ray flux ratio changes
significantly between the prompt and extended emission phase.Comment: A&A letters, in pres
Opening the path to hard X-/soft gamma-ray focussing: The ASTENA-pathfinder mission
Hard X-/soft gamma-ray astronomy is a crucial field for transient, nuclear and multimessenger astrophysics. However, the spatial localization, imaging capabilities and sensitivity of the measurements are strongly limited for the energy range >70 keV. To overcome these limitations, we have proposed a mission concept, ASTENA, submitted to ESA for its program “Voyage 2050”. We will report on a pathfinder of ASTENA, that we intend to propose to ASI as an Italian mission with international participation. It will be based on one of the two instruments aboard ASTENA: a Laue lens with 20 m focal length, able to focus hard X-rays in the 50–700 keV passband into a 3-d position sensitive focal plane spectrometer. The combination of the focussing properties of the lens and of the localization properties of the detector will provide unparalleled imaging and spectroscopic capabilities, thus enabling studies of phenomena such as gamma-ray bursts afterglows, supernova explosions, positron annihilation lines and many more
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