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γ-ray astronomy is the study of the most energetic photons originating in our Galaxy and beyond, and therefore, provides the most direct means of studying the largest transfers of energy occurring in astrophysical processes. The first certain detection of celestialγ-rays came from a satellite experiment flown on OSO-III (Kraushaaret al., 1972); more recently two second generation spark chamberγ-ray telescopes, flown on the SAS-2 (Fichtelet al., 1975) and COS-B (Bennettet al., 1974) satellites, are now obtaining more detailed results on the high energy celestial radiation causingγ-ray astronomy to move from the discovery phase to the exploratory phase. The most striking feature of the celestial sphere when viewed in the frequency range ofγ-rays is the emission from the galactic plane, which is particularly intense in the galactic longitudinal region from 300° to 50°. The longitudinal and latitudinal distributions are generally correlated with galactic structural features and when studied in detail suggest a non-uniform distribution of cosmic rays in the galaxy. Several pointγ-ray sources have now been observed, including four radio pulsars. This last result is particularly striking since only one radio pulsar has been seen at either optical or X-ray frequencies. Nuclearγ-ray lines have been seen from the Sun during a large solar flare and future satellite experiments are planned to search forγ-ray lines from supernovae and their remnants. A general apparently diffuse flux ofγ-rays has also been seen whose energy spectrum has interesting implications; however, in view of the possible contribution of point sources and the observation of galactic features such as Gould's belt, its interpretation must awaitγ-ray experiments with finer spatial and energy resolution, as well as greater sensitivity. Instruments with much greater sensitivity and improved energy and angular resolution are now available and will greatly enhance our understanding of high energy processes in astrophysics, especially in view of the high penetrating power ofγ-rays, which for example permit them to reach the solar system from the far side of the galaxy essentially unattenuated.

0!rQ1The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the ComptonGammaRayObservatoryobserved the Cygnus region in 14 different viewing periods during 1991 May to 1994 July. We present here our results on unpulsed and pulsed emissions of gamma rays at E> 50 MeV from Cyg X-3. While we detect a gamma-ray source consistent with the position of Cyg X-3, there was no evidence for the characteristic ~4.79 hr periodicity observed in X-rays and infrared.

The exciting results from the highly successful Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory (CGRO) has contributed significantly to increasing our understanding of high energy gamma-ray astronomy. A follow-on mission to EGRET is needed to continue these scientific advances as well as to address the several new scientific questions raised by EGRET. Here we describe the work being done on the development of the Advanced Gamma-Ray Astronomy Telescope Experiment (AGATE), visualized as the successor to EGRET. In order to achieve the scientific goals, AGATE will have higher sensitivity than EGRET in the energy range 30 MeV to 30 GeV, larger effective area, better angular resolution, and an extended low and high energy range. In its design, AGATE will follow the tradition of the earlier gamma-ray telescopes, SAS-2, COS B, and EGRET, and will have the same four basic components of an anticoincidence system, directional coincidence system, track imaging, and energy measurement systems. However, due to its much larger size, AGATE will use drift chambers as its track imaging system rather than the spark chambers used by EGRET. Drift chambers are an obvious choice as they have less deadtime per event, better spatial resolution, and are relatively easy and inexpensive to build. Drift chambers have low power requirements, so that many layers of drift chambers can be included. To test the feasibility of using drift chambers, we have constructed a prototype instrument consisting of a stack of sixteen 1/2m × 1/2m drift chambers and have measured the spatial resolution using atmospheric muons. The results on the drift chamber performance in the laboratory are presented here.

The Gamma Ray Observatory (GRO) is currently planned for a launch from the space shuttle in 1990. After the long hiatus in high-energy gamma-ray astronomy since the end of the COS-B mission in 1982, the Soviet missions Granat and Gamma-1 and the NASA mission GRO will resume observations in the energy range from below 100 keV and extending to above 10 GeV. GRO will carry four instruments designed to cover this range of over five decades in photon energy. It is planned to perform a complete sky survey above 1 MeV in the first year of the GRO mission. Data from this survey will be used to study galactic and extragalactic sources of gamma radiation as well as the galactic and extragalactic diffuse emissions. Additionally, measurements of gamma ray bursts will be performed. The angular and spectral resolution of the GRO instruments is significantly improved with respect to previous experiments. The sensitivity for point sources will be better by an order of magnitude, and the location of strong, high energy sources will be determined to about 0.1°–0.2°. After a brief description of the complement of GRO instruments, a detailed discussion of the high-energy telescope EGRET, its design and scientific objectives, is presented in this review.

The all-sky survey in high-energy gamma rays (E> 30 MeV) carried out by EGRET aboard the ComptonGammaRayObservatoryprovides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, as well as an almost uniformly distributed component that is generally believed to originate outside the Galaxy. Through a careful study and removal of the Galactic diffuse emission, the flux, spectrum, and uniformity of the extragalactic emission are deduced. The analysis indicates that the extragalactic emission is well described by a power-law photon spectrum with an index of -(2.10 ± 0.03) in the 30 MeV to 100 GeV energy range. No large-scale spatial anisotropy or changes in the energy spectrum are observed in the deduced extragalactic emission. The most likely explanation for the origin of this extragalactic high-energy gamma-ray emission is that it arises primarily from unresolved gamma-ray-emitting blazars.

The Energetic Gamma Ray Experiment Telescope (EGRET) on the ComptonGammaRayObservatory(CGRO) has so far detected 51 blazars during phases 1, 2, and 3, and cycle 4 of the CGROmission. We present here a summary of these observations, including flux variations and spectra of the blazars. The high luminosities and time variations seen in the gamma-ray data indicate that gamma rays are an important component of the relativistic jet thought to characterize blazars.

Measurements of the flux of helium nuclei in the 24 January, 1971, event and of helium and (C, N, O) nuclei in the 1 September, 1971, event are combined with previous measurements to obtain the relative abundances of helium, (C, N, O), and Fe-group nuclei in these events. These data are then summarized together with previously reported results to show that, even when the same detector system using a dE/dx plus range technique is used, differences in the He/(C, N, O) value in the same energy/nucleon interval are observed in solar cosmic ray events. Further, when the He/(C, N, O) value is lower the He/(Fe-group nuclei) value is also systematically lower in these large events. When solar particle acceleration theory is analyzed, it is seen that the results suggest that, for large events, Coulomb energy loss probably does not play a major role in determining solar particle composition at higher energies (> 10 MeV). The variations in multicharged nuclei composition are more likely due to partial ionization during the acceleration phase.

The primary cosmic-rayα-particle energy spectrum has been investigated, using photographic emulsions flown from Minneapolis on July 30th, 1957. The total flux observed was (151±9)particles/cm2sr s. The differential energy spectrum shows a broad maximum between 400 and 600 MeV/nucleon, and appears different in shape from the spectrum observed at solar minimum. No particles were observed to have kinetic energies below 200 MeV/nucleon, but a substantial flux was observed between 200 and 300 MeV/nucleon. From the centered dipole approximation to the geomagnetic field, one would expect a cut-off energy at this latitude of 292 MeV/nucleon. The results presented here are in disagreement with this figure, but do not allow a choice to be made between cut-off energies predicted from other models.

Numerical values have been calculated for the scattering constant for multiply charged particles in photographic emulsion. The constant has been calculated both with and without cut-off being applied for correction for single scattering, and the results are presented in graphical form. Si sono calcolati i valori numerici della costante di scattering in emulsione fotografica delle particelle con carica multipla. La costante è stata calcolata con e senza la correzione per il cut-off per scattering singolo e i risultati si presentano in grafici.

The general features of the solar particle composition now seem to be clear. The two most abundant components, protons and helium nuclei, have different velocity spectra, similar, but not exactly identical rigidity spectra, and varying relative abundances. The multiply charged nuclei, on the other hand, appear to have the same spectral shape and relative abundances each time measurements are made, at least in the region from 42 to 135 MeV/nucleon. Further, these relative abundances seem to reflect those of the solar atmosphere insofar as comparison can be made. Electrons are rare, but high energy electrons are not expected to be plentiful due to the probable high rate of energy loss caused by synchrotron radiation at the sun. Energetic neutrons were also not expected in large quantity and have not been observed. Finally, there is positive evidence that very small quantities of deuterons exist, probably in an amount which is about 10-3 or less of the proton abundance.

Zusammenfassung Bei chronisch progressiven Tuberkulosen sind vergleichbare Krankheitsdaten, die als Bezugspunkte beispielsweise bei der Untersuchung der chemotherapeutischen Effektivität dienen könnten, schwierig zu gewinnen und meistens mit einer großen Fehlerbreite behaftet. Demgegenüber sind die Sterbedaten eindeutig. Deswegen wurde das durchschnittliche Sterbealter der in der Bundesrepublik Deutschland an den Folgen einer Siliko-Tuberkulose verstorbenen Bergleute untersucht. Die an den Folgen einer Silikose Verstorbenen wurden als Vergleichskollektiv gegenübergestellt. 1954 bis 1964 starben 5310 Bergleute an den Folgen einer Siliko-Tuberkulose, 15695 an den Folgen einer Silikose. Vordem waren die jährlichen Todesfälle wahrscheinlich zahlreicher. Die beiden Kollektive sind aus näher erläuterten Gründen vergleichsweise homogen. Das durchschnittliche Sterbealter bei Siliko-Tuberkulose lag 1964 13,6 Jahre höher als in der Zeit von 1937 bis 1940, 9,6 Jahre höher als 1948. Ziemlich parallellaufend stieg auch das durchschnittliche Sterbealter bei Silikose an. Der Abstand zu dem durchschnittlichen Sterbealter der übrigen Bevölkerung wurde stetig kleiner. Außerdem sank die Siliko-Tuberkulose-Mortalität, wahrscheinlich infolge der abnehmenden Tuberkuloserate bei Silikose. Für das durchschnittliche Sterbealter wurden getrennt für beide Kollektive für die Jahre 1948 bis 1964 Regressionsanalysen durchgeführt und die Gleichungen über ihren Gültigkeitsbereich hinaus bis 1970 extrapoliert. Dadurch ließ sich eine Entwicklung bestimmen mit einem durch Extrapolation ermittelten Anstieg bis etwa 1970. Das errechnete (max.) durchschnittliche Sterbealter der Siliko-Tuberkulose-Kranken beträgt dann 66,0 Jahre, das der Silikose-Kranken 67,5 Jahre. Die Ursachen des Anstieges wurden diskutiert. Außerdem wurde die zeitliche Änderung des durchschnittlichen Sterbealters ermittelt, die mehrere aus dem einfachen Streubereich herausfallende Werte ergab. Für diese Werte boten sich naheliegende Erklärungen an. Durch die Regressionsanalysen und die Bestimmung der zeitlichen Änderung des durchschnittlichen Sterbealters wurden Bezugspunkte gewonnen, die sich bei der Untersuchung von Detail-Entwicklungen als brauchbar erweisen könnten, so bei der Analyse der zur Zeit geübten, aber auch einer gegebenefalls geänderten Chemotherapie.

Low energy celestial gamma ray bursts were discovered1in 1973 and the detection later confirmed by several groups. In this paper we report the low energy gamma-ray bursts ob served by the plastic scintillator anticoincidence dome of the Small Astronomy Satellite-2 (SAS-2) gamma-ray telescope. Although the high energy gamma-ray telescope of SAS-2 has a threshold of about 20 MeV the large SAS-2 anti coincidence dome (A-dome) which is the outermost element of the instrument provides a very large detector for the high energy portion (0.3 MeV) of these burst events.

OBSERVATIONS of electromagnetic radiation from the Crab have been made to at least 1 GeV (ref. 1) and possibly as high as 1012eV (refs 2 and 3). The Crab is unique among strong X-ray sources in that the major component in the low energy range (1–10 keV) shows little or no temporal variation. A small (≲ 10% at 10 keV) pulsed component from NP0532 is observed in the X-ray region, but its strength relative to the constant component increases with increasing X-ray energy. Gamma ray observations of the Crab in the 15–100 MeV range have yielded rather uncertain results with reported upper limits4,5and fluxes6–10in apparent or near conflict. As the reported intensities were just marginally detectable above atmospheric background with the balloon experiments which produced the observations, this seems understandable.