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Plutonium gamma-ray data analysis, in the 100-keV region, using MGA has been improved to overcome the original maximum limit of 2% [SUP238]Pu relative plutonium content in a sample in order to perform an analysis. MGA analysis results of elevated [SUP238]Pu samples are compared to the results from mass spectrometry. [ABSTRACT FROM AUTHOR]

A Medium Energy Gamma-Ray Astronomy (MEGA) detector is being developed and proposed for a small satellite mission. MEGA intends to improve the sensitivity at medium γ-ray energies (0.4-50 MeV) by at least an order of magnitude with respect to past instruments. Its large field of view will be especially important for the discovery of transient sources and for conducting all-sky surveys. Key science objectives for MEGA are the investigation of cosmic high-energy accelerators and of nucleosynthesis sites with γ-ray lines. The large-scale structure of the galactic and cosmic diffuse background is another important goal for this mission. MEGA records and images γ-ray events by completely tracking Compton and pair creation interactions in a stack of double sided Si-strip track detectors and 3-D resolving CsI calorimeters. [ABSTRACT FROM AUTHOR]

The AGILE Mini-Calorimeter (MCAL, with total on-axis radiation length 1.5 X[SUBo]) comprises 2 orthogonal planes each consisting of 16 CsI(T1) bars. Its primary purpose is the energy determination of gamma-rays detected by the Gamma-Ray Imaging Detector (GRID) Tracker (energy range 30 MeV - 50 GeV). In addition, the MCAL is capable of independently triggering and detecting gamma-ray bursts and other impulsive events in the energy range 0.25-250 MeV. A MCAL prototype, comprising 8 CsI(T1) detector elements, was tested both with laboratory sources and with charged particles (p=l GeV/c) during an AGILE Beam Test carried out in November 2000 at the CERN Tll beamline (East Hall, CERN PS). The test setup included a prototype of the electronic chain. A prototype of the digital data acquisition chain, which will be the baseline of the payload Electronic Ground Support Equipment, was also built and tested. We present the preliminary results of this test campaign dedicated to characterizing the detector unit and electronics. [ABSTRACT FROM AUTHOR]

Super-AGILE is the hard X-ray imaging detector of the AGILE gamma-ray mission. It is devoted to monitor X-ray (10-40 keV) sources with an on-axis sensitivity near 5 mCrab in one observing day and to detect X-ray transients in a field of view of 107 deg × 68 deg. Super-AGILE is well matched with the Gamma-Ray Imaging Detector (GRID), and potentially provides source arc-minute positioning depending on intensity, spectrum and background conditions. Super-AGILE detects hard X-rays with one additional layer of four Silicon micro-strip detectors, for 1444 cm[SUP2] total geometrical area. It will be placed on top of the AGILE Tracker and equipped with a system of four mutually orthogonal one-dimentional 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 performance of Super-AGILE as derived by Monte Carlo simulations and experimental tests. [ABSTRACT FROM AUTHOR]

The detection efficiency of EGRET varied throughout the mission due to aging of the spark gas between gas refills, and later in the mission due to partial hardware failures. After the gas refill in 1995 September until the end of the mission in 2000 May, EGRET was operated for approximately 700 days -- several times as long as for earlier gas fills. The efficiency degradation was severe during this time, and it was highly energy dependent affecting the low energies the most. This paper reports on an extensive effort to determine the efficiency factors that apply to data during this period. [ABSTRACT FROM AUTHOR]

AGILE is an ASI gamma-ray astrophysics space Mission which will operate in the 30 MeV - 30 GeV 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. AGILE will be the only Mission entirely dedicated to source detection above 30 MeV during the period 2003-2006. [ABSTRACT FROM AUTHOR]

We present the AGILE REconstruction Method (AREM) and the track finding optimization by Kalman filter algorithms. AREM is a method of γ-ray direction reconstruction to be applied to high-resolution Silicon Tracker detectors in space. It can be used in a "fast mode", independently on Kalman filters techniques, or in an "optimized mode", including Kalman filter algorithms for track identification. AREM correctly addresses three points of the analysis which become relevant for off-axis incidence angles: 1) intrinsic ambiguity in the identification of the 3-D e[SUP+]/e[SUP-] tracks and conversion plane; 2) proper identification of the 3-D reconstructed direction; 3) careful choice of an energy weighting scheme for the 3-D tracks. We present the preliminary results of the angular resolution obtained by analyzing simulated γ-rays in the AGILE detector. The excellent spatial resolution obtained by the AGILE Silicon Tracker allows to improve the angular resolution by a factor ∼2 at energies ≥400 MeV with respect to previous spark chamber detectors (e.g. EGRET). [ABSTRACT FROM AUTHOR]

We present results obtained with a GEANT-based Simulator of the Gamma-Ray Imaging Detector (GRID) developed for the AGILE space astrophysics mission. We describe the AGILE instrument geometry and the model assumed for the charged particle and the albedo-photon backgrounds. Using this simulator, we optimized the event trigger processing. In this paper, we present the main results on different levels of data processing and obtain the background rejection efficiency and the GRID effective area for photon detection in the energy range ∼ 30 MeV - 50 GeV. [ABSTRACT FROM AUTHOR]

AGILE (Light Imaging Detector for Gamma Astronomy) is a satellite for the detection of gamma-ray sources in the energy range 30 MeV - 50 GeV within a large field of view (∼ 1/5 of the sky) and it is planned to fly in the years 2003 - 2006, a period in which no other mission entirely dedicated to photon detection above 30 MeV is planned. AGILE is made of a Tungsten-Silicon Tracker, a CsI Minicalorimeter, an anticoincidence system and a X-ray detector sensitive in the 10 - 40 keV range. The Tracker consists of 14 planes, each one made of 2 layers of 16 single-sided, AC coupled, 410 μm thick, 9.5×9.5 cm[SUP2] Silicon detectors with a readout pitch of 242 μm and a floating strip. The AGILE trigger is generated by the Silicon strips which are readout by the TAA1, a low noise, self triggering ASIC used in a very low power configuration (∼ 400 μW/channel) with analog readout. The number of Tracker readout channels is 43000. We present a description of the Tracker and the performance of the detector (position resolution, cluster pulse height, readout and trigger logic) obtained during three testbeam periods at CERN. [ABSTRACT FROM AUTHOR]

The AGILE scientific instrument is based on an innovative design based on 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 fields of view for the gamma-ray imaging detector (∼3 sr) and Super-AGILE (∼1 sr). [ABSTRACT FROM AUTHOR]

The Ultra-Violet/Optical Telescope (UVOT) provides the Swift Gamma-Ray Burst Explorer with the capability of quickly detecting and characterizing the optical and ultraviolet properties of gamma ray burst counterparts. The UVOT design is based on the design of the Optical Monitor on XMM-Newton. It is a Ritchey-Chrétien telescope with microchannel plate intensified charged-coupled devices (MICs) that deliver sub-arcsecond imaging. These MICs are photon-counting devices, capable of detecting low intensity signal levels. When flown above the atmosphere, the UVOT will have the sensitivity of a 4m ground based telescope, attaining a limiting magnitude of 24 for a 1000 second observation in the white light filter. A rotating filter wheel allows sensitive photometry in six bands spanning the UV and visible, which will provide photometric redshifts of objects in the 1-3.5z range. For bright counterparts, such as the 9th magnitude GRB990123, or for fainter objects down to 17th magnitude, two grisms provide low-resolution spectroscopy. [ABSTRACT FROM AUTHOR]

A Medium Energy Gamma-Ray Astronomy (MEGA) detector is being developed and proposed for a small satellite mission. MEGA intends to improve the sensitivity at medium γ-ray energies (0.4-50 MeV) by at least an order of magnitude with respect to past instruments. Its large field of view will be especially important for the discovery of transient sources and for conducting all-sky surveys. Key science objectives for MEGA are the investigation of cosmic high-energy accelerators and of nucleosynthesis sites with γ-ray lines. The large-scale structure of the galactic and cosmic diffuse background is another important goal for this mission. MEGA records and images γ-ray events by completely tracking Compton and pair creation interactions in a stack of double sided Si-strip track detectors and 3-D resolving CsI calorimeters. [ABSTRACT FROM AUTHOR]

Ground-based telescopes play a role that is complementary to satellite based gamma ray detectors and are expected to provide a rich data set in the 50 GeV-1 TeV region. Heliostat arrays provide a way of making sensitive observations in this energy regime at an economical cost. With close to 2000 heliostat mirrors, the Keck Solar Two Gamma Ray Observatory near Barstow, CA, is the largest such facility in the world, and thus has the potential of being one of the most sensitive gamma ray detectors. A 32-channel camera is now operational: we discuss the current status and future prospects for the instrument. [ABSTRACT FROM AUTHOR]

Preliminary results from CANGAROO-II, a 10 m imaging Cherenkov telescope, in Woomera, South Australia are presented. They include the confirmation of detections of TeV gamma-ray sources we have reported using a 3.8 m telescope, CANGAROO-I. Also the status of the construction of an array of four 10 m telescopes, called CANGAROO-III, is reported. The first telescope of the array was upgraded from the 7 m telescope and the second one is being constructed in this year. The full array will be operating in 2004. [ABSTRACT FROM AUTHOR]

The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) represents a new type of atmospheric Cherenkov detector that achieves a Iow energy threshold for γ-ray detection by using heliostat mirrors in a pre-existing solar research facility. STACEE is designed to study astrophysical sources of γ-rays in the energy range of 50 to 500 GeV. A prototype of the experiment using 32 heliostats (STACEE-32) has previously detected the Crab nebula at high significance, demonstrating the viability of the technique. The completed version of STACEE will use 64 heliostats, and will have a total collection area of ∼ 2300 m[SUP2]. Astrophysics in the 10 to 300 GeV regime has proved to be elusive to both ground-based and satellite experiments and STACEE has the potential of filling an important niche in high energy astrophysics. Here we describe the current status and future goals of STACEE. [ABSTRACT FROM AUTHOR]

Pulse shape discrimination techniques using the scintillator LiBaF[sup 3] allow very clean separation of densely ionizing radiation (protons, tritons, alphas, etc.) from less densely ionizing radiation (electrons). The pulse shape discrimination is based on the presence of sub-nanosecond core-valence luminescence for gammas and electrons. We use a pulse discrimination based on integration of the signal over a short time interval compared to integration over a long time interval. Thermal neutron capture events, fast neutron capture events, and fast neutron elastic scattering events on Li have distinctive loci in a two-dimensional plot of the short gate pulse heights versus total gate pulse heights. Applications of this scintillator include measurements of fast to thermal neutron ratios, fast neutron spectroscopy, and alpha contamination, all in the presence of significant gamma radiation. [ABSTRACT FROM AUTHOR]

Based on the results of detailed modelling of the powerful radio flare of the microquasar GRS 1915+105 in March/April 1994, here we discuss γ-ray fluxes which can be expected from this class of objects. We discuss also perspectives and possible strategy for detection of microquasars in high and very high energy gamma-rays. [ABSTRACT FROM AUTHOR]

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to gamma-ray bursts are beginning operation, and one recently reported evidence for TeV emission from a burst. [ABSTRACT FROM AUTHOR]

The Gamma Ray Large Area Space Telescope (GLAST) is a high energy astronomy mission planned for launch in 2005. GLAST features two instruments; the Large Area Telescope (LAT) operating from 20 MeV - 300 GeV and the Gamma-ray Burst Monitor (GBM) operating from 10 keV - 25 MeV. GLAST observations will contribute to our understanding of active galactic nuclei and their jets, gamma-ray bursts, extragalactic and galactic diffuse emissions, dark matter, supernova remnants, pulsars, and the unidentified high energy gamma-ray sources. The LAT sensitivity is 4 × 10[sup −9] photons cm[sup −2] s[sup −1] (>100 MeV) for a one year all-sky survey, which is a factor of >20 better than CGRO/EGRET. GLAST spectral observations of gamma-ray bursts cover over 6 orders of magnitude in energy thanks to the context observations of the GBM. The upper end of the LAT energy range merges with the low energy end of ground-based observatories to provide a remarkable new perspective on particle acceleration in the Universe. [ABSTRACT FROM AUTHOR]

There is a need for an all sky monitor for flaring TeV γ sources. A modernized version of the wide angle Cherenkov detector AIROBICC promizes to reach a threshold of approx. 2.5 TeV. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ground-based imaging atmospheric Cherenkov telescopes (IACTs) are inherently sensitive to microsecond flares of γ-rays with energies E > 200 MeV. This combination of photon energy and time scale remains largely unexplored by satellite-instruments due to their dead times and collection areas. A burst on a time scale of microseconds could be the signature of the evaporation of a primordial black hole. The technique is based on the detection of multi-photon initiated cascades in the upper atmosphere and could be most effectively pursued with future arrays of imaging telescopes. A first experiment is currently under development: SGARFACE (Short GAmma Ray Front Air Cherenkov Experiment) which consists of a trigger and readout system that can be operated in parallel with the Whipple 10 m telescope. [ABSTRACT FROM AUTHOR]

The last five years have witnessed a rapid increase in the volume of data on proton decaying nuclei. The path was led by decay studies with recoil mass separators equipped with double-sided Si strip detectors. The properties of many proton decaying states were deduced, which triggered renewed theoretical interest in the process of proton decay. The decay experiments were closely followed by in-beam 7-ray studies which extended our knowledge of high-spin states of proton emitters. The unparalleled selectivity of the Recoil-Decay Tagging method combined with the high efficiency of large arrays of Ge detectors allowed, despite small cross sections and overwhelming background from strong reaction channels, the observation of excited states in several proton emitters. Recently, in-beam studies of the deformed proton emitters [sup141]Ho and [sup131]Eu have been performed with the GAMMASPHERE array of Ge detectors and the Fragment Mass Analyzer at ATLAS. Evidence was found for rotational bands in [sup141]Ho and [sup131]Eu. The deformations and the single-particle configurations proposed for the proton emitting states from the earlier proton-decay studies were confronted with the assignments deduced based on the in-beam data. It should be noted that the cross section for populating [sup131]Eu is only about 50 nb, and it represents the weakest channel ever studied in an in-beam experiment [ABSTRACT FROM AUTHOR]

We describe our program to provide cumulative flux limits in the COMPTEL energy range for a large sample of high-energy active galactic nuclei (AGN) of general interest. The First COMPTEL Source Catalogue [1,2] will contain cumulative two-sigma upper limits to the time-averaged MeV-emission measured with COMPTEL for 142 AGN and other unidentified gamma-ray sources detected at high Galactic latitudes (|b|>10°). These limits were derived using composite COMPTEL all-sky maximum-likelihood maps for the 4.5-year period covering Phases 1 through 4 of the CGRO mission (1991–1995). The composite all-sky maps were produced from standard-processing COMPTEL datasets for individual CGRO viewing periods, in four standard energy bins spanning the sensitive range of COMPTEL (0.75–1, 1–3, 3–10, and 10–30 MeV). From these maps we have extracted statistical likelihoods, significances of potential source detections, and associated fluxes, errors, or upper limits, for an extensive list of target objects. In the choice of candidate objects, emphasis was placed on known or suspected gamma-ray sources, particularly those detected in neighboring energy bands to COMPTEL by the CGRO/EGRET and OSSE instruments. These limits will be used to assess the possible contribution of AGN to the diffuse gamma-ray background measured with COMPTEL in the MeV regime. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Milagrito, a detector sensitive to γ-rays at TeV energies, monitored the northern sky during the period February 1997 through May 1998. With a large field of view and high duty cycle, this instrument was used to perform a search for TeV counterparts to γ-rays bursts. Within the Milagrito field of view 54 γ-ray bursts at keV energies were observed by the Burst And Transient Satellite Experiment (BATSE) aboard the Compton Gamma-Ray Observatory. This paper describes the results of a preliminary analysis to search for TeV emission correlated with BATSE detected bursts. Milagrito detected an excess of events coincident both spatially and temporally with GRB 970417a, with chance probability 2.8×10[sup -5] within the BATSE error radius. No other significant correlations were detected. Since 54 bursts were examined the chance probability of observing an excess with this significance in any of these bursts is 1.5×10[sup -3]. The statistical aspects and physical implications of this result are discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Solar Two Gamma-Ray Observatory is designed to close the energy gap between 20–300 GeV that is inaccessible by current instruments, such as the satellite-borne EGRET detector and the ground-based air Cherenkov telescopes. Utilizing the facilities of the Solar Two Power Plant in Barstow, CA, the observatory will detect the Cherenkov light generated as high-energy gamma rays and charged cosmic-ray particles interact with the atmosphere. With over 2000 heliostats available, Solar Two has the largest heliostat mirror area in the world and, thus, the potential to be the most sensitive gamma-ray detector at these energies. Construction of a secondary mirror system capable of imaging 32 heliostats is nearing completion with plans for the first observations of the Crab Nebula in late November. We report on the design, status and testing of this secondary mirror system including the optics, electronics, and heliostat field. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Hard X-Ray Detector (HXD) is one of the instruments on board ASTRO-E, scheduled for lanch in January–February 2000. The HXD consists of 16 Well-type phoswich counters, surrounded by 20 active shield counters (Anti Coincidence Counters: Anti–Counters). It covers the energy range 10–600 keV with a very low background. Because the Anti–Counters are made of thich high-Z material with a very large geometrical area, they retain a large effective area up to high energies. Therefore the Anti–Counters can be used for monitoring high-energy transient sources and γ-ray bursts. In this paper, the all sky monitoring function with the Anti–Counters and the result of their ground calibration tests are described. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A new type of very high energy (> a few 100 GeV) gamma-ray observatory, Milagro, has been built with a large field of view of >1 steradian and nearly 24 hours/day operation. Milagrito, a prototype for Milagro, was operated from February 1997 to May 1998. During the summer of 1998, Milagrito was dismantled and Milagro was built. Both detectors use a 80 m×60 m×8 m pond of water in which a 3 m×3 m grid of photomultiplier tubes detects the Cherenkov light produced in the water by the relativistic particles in extensive air showers. Milagrito was smaller and had only one layer of photomultipliers, but allowed the technique to be tested. Milagrito observations of the Moon’s shadow and Mrk 501 are consistent with the Monte Carlo prediction of the telescopes parameters, such as effective area and angular resolution. Milagro is larger and consists of two layers of photomultiplier tubes. The bottom layer detects penetrating particles that are used to reject the background of cosmic-ray initiated showers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]