G. Simpson

Instrument description and performance of the Imaging Gamma-Ray Telescope COMPTEL aboard the Compton Gamma-Ray Observatory

The imaging Compton telescope COMPTEL is one of the four instruments on board the Compton Gamma-Ray Observatory (GRO), which was launched on 1991 April 5 by the space shuttle Atlantis into an Earth orbit of 450 km altitude. COMPTEL is exploring the 1-30 MeV energy range with an angular resolution (1σ) between 1° and 2° within a large field of view of about 1 steradian. Its energy resolution (8.8% FWHM at 1.27 MeV) makes it a powerful gamma-ray line spectrometer. Its effective area (for on-axis incidence) varies between 10 and 50 cm 2 depending on energy and event selections. Within a 14 day observation period COMPTEL is able to detect sources which are about 20 times weaker than the Crab. The measurement principle of COMPTEL also allows the measurements of solar neutrons

The Imaging Compton Telescope Comptel on the Gamma Ray Observatory

This instrument is based on a newly established concept of ¿-ray detection in the very difficult 1-30 MeV range. It employs the unique feature of a two-step interaction of the y-ray: a Compton scattering collision in a first detector followed by an interaction in a second detector element. COMPTEL has been designed to perform a very sensitive survey of the y-ray sky. Extreme care has been taken to minimize background so that the detection limits of COMPTEL will be dominated by source counting statistics. It combines a wide field of view (about 1 steradian) with a good angular resolution. The design criteria of COMPTEL and the perforrmance of a Science Model are described.

COMPTEL as a Solar Gamma Ray and Neutron Detector

The imaging Compton telescope COMPTEL on the Gamma Ray Observatory has unusual spectroscopic capabilities for measuring solar γ-ray and neutron emissions. Flares can be observed above the 800 keV γ-ray threshold of the telescope. The telescope energy range extends to 30 MeV with high time resolution burst spectra available from 0.1 to 10 MeV. Strong Compton tail suppression facilitates improved spectral analysis of solar flare γ-ray emissions. In addition, the high signal-to-noise ratio for neutron detection and measurement provides new neutron spectroscopic capabilities. For example, a flare similar to that of 1982 June 3 will yield spectroscopic data on > 1500 individual neutrons, enough to construct an unambiguous spectrum in the energy range of 20 to 150 MeV. Details of the instrument response to solar γ-rays and neutrons are presented.

The GRO - COMPTEL Mission: Instrument Description and Scientific Objectives

The imaging Compton telescope COMPTEL is one of the four instruments onboard NASA’s Gamma Ray Observatory GRO which is to be launched in April 1991 by the Space Shuttle Atlantis. COMPTEL will explore the 1 to 30 MeV energy range with an angular resolution of a few degrees within a large field-of-view of about 1 steradian. Its medium energy resolution (8.8% FWHM at 1.27 MeV) in addition makes it to a powerful gamma-ray line spectrometer. Within a 2-weeks observation period COMPTEL will be able to detect sources which are about 20-times weaker than the Crab. With these properties COMPTEL is well suited to perform the first complete sky survey at MeV-energies. Targets of special interest are galactic gamma ray sources (like radio pulsars, X-ray binaries, the Galactic Center, the unidentified COS-B sources, supernova remnants and molecular clouds), external galaxies (especially the nuclei of active galaxies), gamma-ray line sources (e.g. the distribution of the 1.8 MeV line emissivity throughout the Galaxy), the diffuse gamma-ray emission from interstellar space, the cosmic gamma-ray background, cosmic gamma-ray bursts, and gamma-ray and neutron emission during solar flares.

Gamma-ray burst detection capabilities of comptel

Abstract The imaging gamma-ray telescope COMPTEL, capable of detecting gamma rays in the 1 to 30 MeV range, is one of four experiments onboard NASAs Gamma-Ray Observatory GRO. Besides its primary objectives COMPTEL will contribute to the understanding of cosmic gamma-ray bursts. Summarising, COMPTEL localises bursts (S (E > 1 MeV) ≥ 2.10 −6 erg/cm 2 ) within 1 sr FOV to better than 1° at medium gamma-ray energies, measures continuum energy spectra in the range 0.1 MeV to 20 MeV with fluence S ≥ 6.9 10 −7 erg/cm 2 (5 σ , E≥100 keV), measures gamma-ray lines with detector resolution 9.6% (at 0.5 MeV) and 7.0% (at 1.5 MeV) and determines time histories of both gamma-ray line and continuum emission with t ≥ 0.1 sec resolution.

Neural Net Approaches for Event Location in the Detector Modules

From the description of the Compton telescope given previously (Schonfelder et al., this volume), one can see that the accuracy with which one determines the position of a cosmic gamma-ray source depends not only on the measurements of the energy deposited in the upper (D1) and lower (D2) detectors, but also on how accurately one estimates the (X, Y, Z) positions of each gamma-ray or neutron interaction (an event). If nothing were known about the position of each event except in which module it occured, it would increase the uncertainty in the position of a source by on the order of 10°. Within each COMPTEL module, one extracts position information from comparisons of relative intensities of signals in the photomultipier tubes. This technique was introduced in the 1950’s for medical imaging by Anger (1958), and later was adapted to astrophysical applications (Zych et al. 1983; Schonfelder et al. 1984; Stacy 1985).

COS-B gamma ray sources beyond the predicted diffuse emission

Abstract The “2CG” gamma-ray point-source catalog was established before galactic surveys of the CO-line emission tracing molecular hydrogen became available. With the complete galactic HI and CO surveys which are now available, it has become possible to remove the effect of “galactic diffuse” emission from point source catalogs discriminating those sources which are either compact objects or very local and strong enhancements in the galactic cosmic-ray distribution from those which are artifacts due to the structured gas distribution. A new methodology has been developed for this purpose with the following three features: automatic generation of source catalogs using correlation analysis, simulation of trials to derive catalog significance thresholds, and bootstrap sampling to derive confidence intervals for source parameters. The analysis reported here shows that about half of the 2CG sources are explained by concentrations in the distribution of molecular hydrogen, and it reports the discovery of several new rather weak sources.

COMPTEL Processing and Analysis Software System: COMPASS (Requirements and Overview)

In this paper the COMPTEL Processing and Data Analysis System COMPASS is described. A general overview of the system software is given with a focus on the software engineering aspects.

COMPASS: the COMPTEL Processing and Analysis Software Software System

We describe the features of the COMPASS, the system for the processing and analysis of data from COMPTEL a gamma-ray telescope which will be put into orbit onboard the NASA Gamma-Ray Observatory. The main features of the COMPASS are: high host system independence, data integrity maintenance facilities, a menu-controlled user shell, and data access via data abstractions.