Guido Di Cocco

Detection of terrestrial gamma ray flashes up to 40 MeV by the AGILE satellite

We report the detection by the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite of terrestrial gamma ray flashes (TGFs) obtained with the minicalorimeter (MCAL) detector operating in the ...

MAX: a gamma-ray lens for nuclear astrophysics

The mission concept MAX is a space borne crystal diffraction telescope, featuring a broad-band Laue lens optimized for the observation of compact sources in two wide energy bands of high astrophysical relevance. For the first time in this domain, gamma-rays will be focused from the large collecting area of a crystal diffraction lens onto a very small detector volume. As a consequence, the background noise is extremely low, making possible unprecedented sensitivities. The primary scientific objective of MAX is the study of type Ia supernovae by measuring intensities, shifts and shapes of their nuclear gamma-ray lines. When finally understood and calibrated, these profoundly radioactive events will be crucial in measuring the size, shape, and age of the Universe. Observing the radioactivities from a substantial sample of supernovae and novae will significantly improve our understanding of explosive nucleosynthesis. Moreover, the sensitive gamma-ray line spectroscopy performed with MAX is expected to clarify the nature of galactic microquasars (e+e- annihilation radiation from the jets), neutrons stars and pulsars, X-ray Binaries, AGN, solar flares and, last but not least, gamma-ray afterglow from gamma-burst counterparts.

The AGILE Instrument

AGILE is an ASI gamma-ray astrophysics space Mission which will operate in the 30 MeV - 50 GeV range with imaging capabilities also in the 10 - 40 keV range. Primary scientific goals include the study of AGNs, gamma-ray bursts, Galactic sources, unidentified gamma-ray sources, diffuse Galactic and extragalactic gamma-ray emission, high-precision timing studies, and Quantum Gravity testing. The AGILE scientific instrument is based on an innovative design of three detecting systems: (1) a Silicon Tracker, (2) a Mini-Calorimeter, and (3) an ultralight coded mask system with Si-detectors (Super-AGILE). AGILE is designed to provide: (1) excellent imaging in the energy bands 30 MeV-50 GeV (5-10 arcmin for intense sources) and 10-40 keV (1-3 arcmin); (2) optimal timing capabilities, with independent readout systems and minimal deadtimes for the Silicon Tracker, Super-AGILE and Mini-Calorimeter; (3) large field of view for the gamma-ray imaging detector (~3 sr) and Super-AGILE (~1 sr). AGILE will be the only Mission entirely dedicated to source detection above 30 MeV during the period 2004-2006.

PICsIT: the high-energy detection plane of the IBIS instrument onboard INTEGRAL

IBIS is one of the two main instruments onboard the INTEGRAL gamma-ray satellite. IBIS will produce images of the gamma- ray sky in the region between 15 keV and 10 MeV by means of a coded mask coupled to a double-layer position sensitive detector. PICsIT is the detection layer optimized for high energy. It has a total area of 3065 cm2 and is composed by 4096 individual pixels made of CsI(Tl) crystal, each one with its proper electronic chain. The single units are 0.75 cm2 in area, and 3 cm thick. The front end electronics are designed so that analogue circuits, with their low noise figure, will allow the exploitation of the spectroscopic characteristics of the detector. The digital circuits will allow PICsIT to operate in anticoincidence with an active shield, and to deliver the interaction time of occurrence of the events.

Monitoring the hard X-ray sky with SuperAGILE

Context SuperAGILE is the hard X-ray monitor of the AGILE gamma ray mission, in orbit since 23 April 2007. It is an imaging experiment based on a set of four independent silicon strip detectors, eq ...

Design and flight performance of a crystal diffraction telescope

We present the design and performance of the gamma-ray lens telescope CLAIRE, which flew on a stratospheric balloon on June 14, 2001. The objective of this project is to validate the concept of a Laue diffraction lens for nuclear astrophysics. Instruments of this type, benefiting from the dramatic improvement of the signal/noise ratio brought about by focusing, will combine unprecedented sensitivities with high angular resolution. CLAIREs lens consists of Ge-Si mosaic crystals, focusing gamma-ray photons from its 505 cm2 area onto a small solid state detector, with only 7.2 cm3 volume for background noise. The diffracted energy of 170 keV results in a focal length of 279 cm, yet the entire payload weighed under 500 kg. CLAIRE was launched by the French Space Agency (CNES) from its balloon base at Gap in the French Alps (Southeast of France) and was recovered near Bordeaux in the Southwest of France after roughly 5 hours at float altitude. After presenting the principle of a diffraction lens, the CLAIRE 2001 flight is analyzed in terms of pointing accuracy, background noise and diffraction efficiency of the lens.

Spectroscopy and polarimetry capabilities of the INTEGRAL imager: Monte Carlo simulation results

A three-dimensional position sensitive imaging detector has been proposed for the prospective ESA/NASA gamma-ray satellite, INTEGRAL. The instrument is based on two layers of bar shaped CsI(T1) crystals viewed by photodiodes. The GEANT3 Monte Carlo simulation package has been used to assess the spectroscopic and enhanced imaging performance of this detector and an original routine has been written to assess its capabilities as a Compton polarimeter. A description of the algorithm of this routine is given with the results of both GEANT3 and the polarization simulations.

In-flight performance of the AGILE mini-calorimeter and its gamma-ray burst detection capabilities

The Minicalorimeter (MCAL) is a scintillation detector onboard the Italian space mission AGILE, dedicated to gamma-ray and hard-X astrophysics and launched on 23 April, 2007. MCAL can work both as part of the gamma-ray imaging system and as an independent detector for gamma-ray burst (GRB) in the 350 keV - 100 MeV energy range. The on-board trigger logic is now enabled for burst search on timescales as short as 64 ms, leading to a detection rate of about one event/week. MCAL is particularly suitable for the detection of short-hard bursts and contributes to GRB localization through the Inter-Planetary Network (IPN).

Scientific calibration of the PICsIT engineering model detector of the IBIS telescope

IBIS is the imaging telescope onboard the ESA satellite INTEGRAL, which will be launched in September, 2001. IBIS will produce images of the gamma-ray sky in the region between 15 keV and 10 MeV by means of a position sensitive detection lane coupled with a coded aperture mask. The detection plane of IBIS comprises two position sensitive layers: ISGRI and PICsIT. PICsIT is a 64 X 64 unit array of approximately equals 0.75 cm2 crystals operative in the energy range between 150 keV and 10 MeV. The engineering model (EM) of PICsIT has now been calibrated and delivered to ESA. In this work we present the preliminary results obtained from the PICsIT EM scientific calibrations. These test were the first occasion for measuring the general behavior of the detector in terms of the key scientific performances. The gain, linearity, energy resolution, lower energy threshold and background counting rate for each detection unit and the variation of these parameters as a function of pixel position and were measured. Preliminary results regarding event multiplicity distribution, and energy resolution degradation for multiple events are also presented.

In-flight calibration requirements for the PICsIT high-energy imaging detector

IBIS is the high energy imagin telescope onboard the ESA satellite INTEGRAL, which will be launched in September 2001. The detection p;lane of IBIS comprises two position sensitive layers: ISGRI and PICsIT. PICsIT consists of a 64 X 64 unit array of approximately equals 0.8 cm2 crystals operating in the energy range between 150 keV and 10 MeV. Due to the low intrinsic signal-to-noise ratio of the cosmic sources in the gamma-ray domain, INTEGRAL observing times will be very long, lasting about 105-106 s. Moreover, the image formation principle on which PICsIT works is that of coded aperture imaging in which the entire detection plane contributes to each decoded sky pixel. For these two reasons, the spatial and temporal uniformity in gain, linearity and energy resolution of the individual detection units is of paramount importance for fully exploiting the capabilities of the instrument. In IBIS this is accomplished by having onboard a low-intensity tagged radioactive source constantly illuminating the entire detection plane with 511 and 1275 keV energy photons. Herein we describe the scientific rationale and requirements of the in-flight calibration system from the point of view of the high energy detector PICsIT, and the impact on the PICsIT scientific performance as a function of the overall calibration accuracy achieved during the flight.