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We are designing MARGIE as a 100 day ULDB mission to: a) detect and localize gamma-ray bursts; and b) survey the hard X-ray sky. MARGIE will consist of one small field-of-view (FOV) and four large FOV coded mask modules mounted on a balloon gondola. The burst position will be calculated onboard and disseminated in near-real time, while information about every count will be telemetered to the ground for further analysis. In a 100-day mission we will localize ∼40 bursts with peak photon fluxes from 0.14 to ∼5 ph cm-2 s-1 using 1 s integrations; the typical localization resolution will be better than ∼2 arcminutes. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

FiberGLAST is one of several instrument concepts being developed for possible inclusion as the primary Gamma-ray Large Area Space Telescope (GLAST) instrument. The predicted FiberGLAST effective area is more than 12,000 cm2 for energies between 30 MeV and 300 GeV, with a field of view that is essentially flat from 0°–80°. The detector will achieve a sensitivity more than 10 times that of EGRET. We present results of simulations that illustrate the sensitivity of FiberGLAST for the detection of gamma-ray bursts. © 2000 American Institute of Physics. [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]

MARGIE (Minute-of-Arc Resolution Gamma-ray Imaging Experiment) is a large area (∼10[sup 4] cm[sup 2]), wide field-of-view (∼1 sr), hard X-ray/gamma-ray (∼20–600 keV) coded-mask imaging telescope capable of performing a sensitive survey of both steady and transient cosmic sources. MARGIE has been selected for a NASA mission-concept study for an Ultra Long Duration (100 day) Balloon flight. We describe our program to develop the instrument based on new detector technology of either cadmium zinc telluride (CZT) semiconductors or pixellated cesium iodide (CsI) scintillators viewed by fast-timing bi-directional charge-coupled devices (CCDs). The primary scientific objectives are to image faint Gamma-Ray Bursts (GRBs) in near-real-time at the low intensity (high-redshift) end of the logN-logS distribution, thereby extending the sensitivity of present observations, and to perform a wide field survey of the Galactic plane. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report a refined analysis of the cosmic diffuse gamma-ray background (hereafter CDG) in the energy range 0.8–30 MeV with the Compton telescope COMPTEL onboard the Compton Gamma-Ray Observatory. We have identified all major instrumental-background lines, included the results of a detailed study of the instantaneous instrumental continuum-background characteristics, and used all available COMPTEL data at high galactic latitudes. The new “whole-sky” average CDG spectrum again shows no evidence for an MeV-bump, merges smoothly with the spectra at higher and lower energies, and is consistent with a transition from a softer to a harder component around a few MeV. This spectrum is consistent with previous COMPTEL results. In addition, comparison of the CDG intensity from various regions of the sky allows us to place limits on the large-scale anisotropy of the CDG in selected energy bands. Upper limits on the relative deviations from isotropy consistent with the data at the 95% confidence limit range from about 24% to about 45% on scales of a few steradian. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The instrumental-line background of the Compton telescope COMPTEL onboard the Compton Gamma-Ray Observatory is due to the activation and/or decay of a number of different isotopes. The major components of the COMPTEL instrumental-line background can be attributed to eight individual isotopes, namely [sup 2]D, [sup 22]Na, [sup 24]Na, [sup 28]Al, [sup 40]K, [sup 52]Mn, [sup 57]Ni, and [sup 208]Tl. In addition, evidence for the presence of [sup 27]Mg has been obtained in the search for gamma-ray lines from supernovae. The identification of the instrumental lines with specific isotopes is based on the line energies as well as on the variation of the activity with time, cosmic-ray intensity and deposited radiation dose during passages through the South-Atlantic Anomaly. The characteristic variation of the activity due to an individual isotope depends on its life-time, orbital parameters, and the solar cycle. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]