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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 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.

As the instrumental resolution of high-energy astronomical experiments increases, the observer is confronted with a ’space of outcomes’ (hereafter dataspace) with at most a few events per bin (particularly if time resolution comes into play). This implies that the sought signal is not only contaminated by additive noise components (e.g. instrumental, earth’s atmosphere), but is also masked by relatively large intrinsic statistical fluctuations. In the case of the 1–30 MeV imaging telescope COMPTEL, the number of counts per bin is of the order 1, if the full resolution is to be explored.

The COMVIEL telescope onboard the NASA Gamma Ray Observatory is an instrument with imaging properties quite different from telescopes at longer wavelengths: Focusing of the incoming radiation is impossible due to the penetrating power of the gamma ray photons, the photons rather interact with the electrons and nuclei of the detector material in a particle-like manner. This affects the way the response of the instrument is described, determined, and used. The instrument consists of 2 planes of detector modules, which measure a photon via two consecutive interactions of probabilistic nature: a Compton scatter in the upper detector plane (’D1’), and an absorption in the lower detector plane (’D2’) (see figure 1). The active scintillation detectors are surrounded by plastic anticoincidence detector domes to reject events originating from charged particles. Background events are suppressed by measurement of the pulse shape of the scintillation light flash in the upper detectors, and by measurement of the time of flight of the scattered photon from upper to lower detector plane.

The imaging γ‐ray telescope COMPTEL on board NASA’s Compton Gamma‐Ray Observatory (GRO) has observed many cosmic gamma‐ray bursts during the early mission phase of GRO. COMPTEL records time‐resolved burst spectra over 0.1 MeV to 10 MeV energies, and, for the first time, produces direct single‐telescope gamma‐ray images (0.8–30 MeV) of cosmic gamma‐ray bursts occurring in its 1 sr field of field.

The γ‐ray telescope COMPTEL onboard GRO has so far located 6 gamma‐ray bursts which occurred in its ∼1 sr field of view. The positions of the sources were derived by the maximum‐entropy method. Systematic and statistical uncertainties for the four strongest bursts are approximately 1° to 2° and can be reduced in future analysis.

On 1993 January 31 at 1857:12 Universal Time (UT), the Imaging Compton Telescope COMPTEL onboard the Compton Gamma Ray Observatory (CGRO) detected the cosmic gamma-ray burst GRB 930131. COMPTEL's MeV imaging capability was employed to locate the source to better than 2 deg (1 sigma error radius) within 7 hr of the event, initiating a world-wide search for an optical and radio counterpart. The maximum likelihood position of the burst from the COMPTEL data is alpha(sub 2000) = 12h 18m, delta(sub 2000) = -9 deg 42 min, consistent with independent CGRO-Burst and Transient Source Experiment (CGRO-BATSE) and Energetic Gamma Ray Experiment Telescope (EGRET) locations as well as with the triangulation annulus constructed using BATSE and Ulysses timing data. The combined COMPTEL and EGRET burst data yield a better estimate of the burst location: alpha(sub 2000) = 12h 18m and delta(sub 2000) = -10 deg 21 min, with a 1 sigma error radius of 32 min. In COMPTEL's energy range, this burst was short, consisting of two separate spikes occurring within a approximately 1 s interval with a low intensity tail for approximately 1 s after the second spike. No statistically significant flux is present for a 30 s period after the main part of the burst. This is consistent with the EGRET data. The COMPTEL telescope events indicate a hard, power-law emission extending to beyond 10 MeV with a spectral index of -1.8 +/- 0.4. The rapid fluctuations and high intensities of the gamma-ray flux greater than 10 MeV place the burst object no farther than 250 pc if the burst emission is not beamed.

The relationship between flux in the 847 keV line and optical (B) magnitude is examined for the two Type Ia supernovae (SNe Ia) observed so far in the γ-ray domain. This type of analysis allows us to discriminate between possible models for a given SN Ia event. In the case of SN 1991T in NGC 4527, in view of the constraints provided by CGRO on the flux of the 847 keV line and the B-magnitude of the supernova at the phase of the gamma-ray observation it is possible to discard many of the SN Ia models so far proposed. Models giving rise to a γ-ray escape fraction larger than 80% at 70-80 days after explosion do not fall within the validity region of the 847 keV flux-mg diagram

The imaging gamma-ray telescope COMPTEL, capable of detecting gamma rays in the 1 to 30 MeV range, is one of four experiments onboard NASA's 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.

The contribution of normal spiral galaxies to the high galactic latitude gamma-ray background >100 MeV is examined in the light of the estimates of its flux from the SAS-II measurements. The gamma-ray luminosity of each object is inferred from the known Milky Way value normalized to the corresponding optical quantity. Several possibilities are considered for the responsible physical production mechanism both diffuse and localized; they are then set to evolve with the galactic age according to three well-known evolutionary models. A final space-time integration leads to results which are expressed in the same unit as the measured background. It is seen that the model presented here can play an important role in the region > 100 MeV where the information on the spectral shape of the radiation is still very poor. Experimental tests for future gamma-ray observations are presented.

One of the scientific objectives of NASA's Fermi Gamma-ray Space Telescope is the study of Gamma-Ray Bursts (GRBs). The Fermi Gamma-Ray Burst Monitor (GBM) was designed to detect and localize bursts for the Fermi mission. By means of an array of 12 NaI(Tl) (8 keV to 1 MeV) and two BGO (0.2 to 40 MeV) scintillation detectors, GBM extends the energy range (20 MeV to > 300 GeV) of Fermi's main instrument, the Large Area Telescope, into the traditional range of current GRB databases. The physical detector response of the GBM instrument to GRBs is determined with the help of Monte Carlo simulations, which are supported and verified by on-ground individual detector calibration measurements. We present the principal instrument properties, which have been determined as a function of energy and angle, including the channel-energy relation, the energy resolution, the effective area and the spatial homogeneity., 36 pages, 28 figures, accepted for publication in Experimental Astronomy

The COS-B satellite has observed the X-ray source Cen X-3 in the energy range 2 to 12 keV

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.

SPI (Spectrometer for INTEGRAL) is a high spectral resolution gamma-ray telescope to be flown on board the ESA mission INTEGRAL. It consists of an array of 19 closely packed Germanium detectors surrounded by an active anticoincidence shield of EGO. The imaging capabilities of the instrument are obtained with a tungsten coded aperture mask located 1.7 m from the Ge array. The fully coded field-of-view is 16 degrees and the angular resolution approximate to 2 degrees. The energy range extends from 20 keV to 8 MeV with a typical energy resolution approximate to 2 keV at 1 MeV. The point-source narrow-line sensitivity is estimated to be (3-7) x 10(-6) ph/cm(-2) s(-1) over most of the energy range of the instrument (E > 200 keV) for a 10(6) s observing time. With these expected performances a major step forward can be expected in fine gamma-ray spectroscopy of astrophysical objects.

The spectrometer on INTEGRAL (SPI) is one of the two main telescopes of the future INTEGRAL observatory. SPI is made of a compact hexagonal matrix of 19 high-purity germanium detectors shielded by a massive anticoincidence system. A HURA type coded aperture modulates the astrophysical signal. The spectrometer system, its physical characteristics and performances are presented. The instrument properties such as imaging capability, energy resolution and sensitivity have been evaluated by means of extensive Monte-Carlo simulations. With the expected performances of SPI, it will be possible to explore the γ-ray sky in greater depth and detail than it was possible with previous γ-ray telescopes like SIGMA, OSSE and COMPTEL. In particular, the high-energy resolution will allow for the first time the measurement of γ-ray line profiles. Such lines are emitted by the debris of nucleosynthesis and annihilation processes in our Galaxy. Lines from these processes have already been measured, but due to the relatively ...

The International Gamma-ray Astrophysics Laboratory (INTEGRAL) is conceived as the next logical step in gamma-ray astronomy after the US Compton Gamma-Ray Observatory (CGRO) and the French/Russian SIGMA mission. The INTEGRAL scientific payload consists of two main instruments (Imager and Spectrometer) and two monitor instruments (X-Ray Monitor and Optical Transient Camera). The INTEGRAL spectrometer "SPI" is optimized for detailed measurements of gamma-ray lines and mapping of diffuse sources. It combines a coded aperture mask with an array of large volume, high-purity germanium detectors. The detectors make precise measurements of the gamma-ray energies over the 20 keV-8 MeV energy range. This paper presents the instrument characteristics these properties have been evaluated by means of Monte Carlo calculations. With the characteristic features It will be possible to study gamma-ray emission from compact objects or line profiles with a high-energy resolution and a good angular resolution.

The Fermi Gamma-ray Burst Monitor (GBM) is designed to enhance the scientific return from Fermi in studying gamma-ray bursts (GRBs). In its first two years of operation GBM triggered on 491 GRBs. We summarize the criteria used for triggering and quantify the general characteristics of the triggered GRBs, including their locations, durations, peak flux, and fluence. This catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC)., Comment: 92 pages, 11 figures, 5 tables; to be published in ApJS

LOCALISED γ-ray sources contribute to the overall galactic emission; some of these sources have been identified with known astronomical objects1,2, while several unidentified γ-ray sources have also been reported3,4. We describe here a search for γ-ray sources using data from the ESA γ-ray satellite COS B which revealed 10 new unidentified sources. These sources seem to be galactic with typical γ-ray luminosities above 100 MeV in excess of 1035 erg s−1.

DURING the past two years results from two different balloon experiments1,2 indicate that the γ-ray emission from the Crab Nebula between 1 and 10 MeV is considerably above the straight line interpolation from lower and higher photon energies. The excess above the power law has been claimed to be factor of 7 between 1 and 3 MeV and of a factor 30 between 3 and 10 MeV. The fact that both experiments yielded nearly identical results gives support to the reality of the excess component. The power in this excess is nearly as large as the total integrated synchrotron power of 2×10−7 erg cm−2 s−1 of the Crab Nebula. It has been speculated that this powerful, narrow-band component may be produced in the pulsar magnetosphere, possibly near the surface of the neutron star2.