Marcello Mastropietro

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.

The Basic Unit of the Imaging Plane of the ZEBRA Low Energy Gamma Ray Telescope

The mechanical, elecrtical, and performance characteristics of one element of the ZEBRA telescopes position sensitive aetection plane are presented. One unit comprises a NaI(Tl) bar 55×5,8×5 cm thick and two photomultiplier tubes one mounted on each end. The surface of the bar has been treated to enhance the exponential attenuation of the scintillation light produced by an event. The signal from the two tubes are taken in coincidence and, by the application of two simple algoritms, the energy and position of the event along the bar can be calculated. The tubes are powered by two programmable low consumption high tension supplies. Their digital control makes automatic gain correction feasible during the flight.

POLARIX: a small mission of x-ray polarimetry

X-Ray Polarimetry can be now performed by using a Micro Pattern Gas Chamber in the focus of a telescope. It requires large area optics for most important scientific targets. But since the technique is additive a dedicated mission with a cluster of small telescopes can perform many important measurements and bridge the 40 year gap between OSO-8 data and future big telescopes such as XEUS. POLARIX has been conceived as such a pathfinder. It is a Small Satellite based on the optics of JET-X. Two telescopes are available in flight configuration and three more can be easily produced starting from the available superpolished mandrels. We show the capabilities of such a cluster of telescopes each equipped with a focal plane photoelectric polarimeter and discuss a few alternative solutions.

Design and performance of a one square meter proportional counter system for hard x-ray astronomy

A versatile balloon borne hard X-ray experiment with a very large area (≈1.1 m2) and high spectral resolution has been developed for the study of the hard X-ray sources in the energy range 20–180 keV. The telescope consists of four multiwire proportional chambers (MWPC) that have a geometrical sensitive area of 2700 cm2 each. The detector system has a sensitivity of ≈10−5 photons cm−2s−1 keV−1 during a typical ballon observation. A background rate of ≈3×10−4 counts cm−2s−1 keV−1 was observed in the operative energy range at 2.4 gm/cm2 ceiling altitude and geographic latitude of 38°N. The design details, fabrication and flight performance of the instrument are briefly discussed with reference to the effectiveness of background reduction and other test parameters.

Scientific performances of the XAA1.2 front-end chip for silicon microstrip detectors

The XAA1.2 is a custom ASIC chip for silicon microstrip detectors adapted by Ideas for the SuperAGILE instrument on board the AGILE space mission. The chip is equipped with 128 input channels, each one containing a charge preamplifier, shaper, peak detector and stretcher. The most important features of the ASIC are the extended linearity, low noise and low power consumption. The XAA1.2 underwent extensive laboratory testing in order to study its commandability and functionality and evaluate its scientific performances. In this paper we describe the XAA1.2 features, report the laboratory measurements and discuss the results emphasizing the scientific performances in the context of the SuperAGILE front-end electronics.

A versatile facility for the calibration of X-ray polarimeters with polarized and unpolarized controlled beams

We devised and built a versatile facility for the calibration of the next generation X-ray polarimeters with unpolarized and polarized radiation. The former is produced at 5.9 keV by means of a Fe55 radioactive source or by X-ray tubes, while the latter is obtained by Bragg diffraction at nearly 45 degrees. Crystals tuned with the emission lines of X-ray tubes with molybdenum, rhodium, calcium and titanium anodes are employed for the efficient production of highly polarized photons at 2.29, 2.69, 3.69 and 4.51 keV respectively. Moreover the continuum emission is exploited for the production of polarized photons at 1.65 keV and 2.04 keV and at energies corresponding to the higher orders of diffraction. The photons are collimated by means of interchangeable capillary plates and diaphragms, allowing a trade-off between collimation and high fluxes. The direction of the beam is accurately arranged by means of high precision motorized stages, controlled via computer so that long and automatic measurements can be done. Selecting the direction of polarization and the incidence point we can map the response of imaging devices to both polarized and unpolarized radiation. Changing the inclination of the beam we can study the systematic effects due to the focusing of grazing incidence optics and the feasibility of instruments with large field of view.

High pressure MWPC for hard X-ray astronomy

Abstract The second generation of detectors for hard X-ray astronomy essentially requires large area detectors and efficient background discrimination. A conventional scheme is to use an array of NaI scintillator crystals with a large number of photomultipliers, a light collection system and individual guard counters for charged particle rejection. High pressure proportional counters can provide an alternative instrument with comparatively higher performance in terms of effective area and background discrimination at lower cost and weight. A 900 cm 2 detector, with a thin aluminium window (0.16 g/cm 2 ) and a 4 atm xenon filling has been developed and tested on a balloon flight.

Instrumental and astrophysical performances of SuperAGILE on-board AGILE Gamma-Ray mission

SuperAGILE is the X-ray stage of AGILE gamma-ray mission. It is devoted to monitor X-ray (10 - 40 keV) sources with a sensitivity better than 10 mCrab in one observing day and to detect X-ray transients in a field of view of 1.8 sr, well matched to that of the gamma ray tracker, with few arc-minutes position resolution. SuperAGILE is designed to exploit one additional layer of four silicon micro-strip detectors, for 1444 cm2 of total geometrical area, on top of the AGILE tracker and a system of four mutually orthogonal one- dimensional coded masks to encode the X-ray sky. Low noise electronics based on ASICs technology is the front-end read out. We present here the instrumental and astrophysical performances of SuperAGILE as derived by Monte Carlo simulation and experimental tests.

An imaging escape gated MWPC for hard X-ray astronomy

Abstract A scientific forward step in the hard X-ray and soft gamma-ray astronomy will only be possible with the use of a new generation of space borne instruments. Their main characteristics have to the two-dimensional imaging capability over a large collecting area and the fine spectral resolution in order to discriminate between the weak signal coming from cosmic sources to be detected and the strong background induced by cosmic rays, in the space environment, on the detector. To reach this goal we have developed a new hard X-ray position sensitive proportional counter operating with the escape gate technique in the range 15–150 keV, to be used together with a pseudo-random coded mask in order to obtain sky images. The detector is a high pressure (5 bar) xenon-argon-isobutane filled chamber with a spatial resolution of 30 × 2 mm and a spectral resolution of 5% at 60 keV on the sensitive area of 3000 cm 2 .

A position-sensitive semi-proportional chamber for ultra-soft x-rays

Abstract A straightforward approach to the problem of obtaining position measurements from a soft X-ray (0.1–6 keV) proportional counter is presented in this paper. The characteristics of the chamber and the noise degradation of the spatial resolution at lower energies are discussed.