Brief discussion of the necessity to carry out gamma-ray observations in the uninvestigated energy range 5-400 GeV by instrument on the board of space vehicle is given. One of the possible versions of such gamma-telescope is described and some estimations of the possible statistics are made.
State of Observations in Gamma-Ray AstronomyObservations of celestial gamma-radiation cover a wide energy range: from the lowest energies that are still called ~,-rays (hundreds of keV) up to approximately 1016 eV. In the energy range from 50-70 MeV up to GeV the main information about gammaradiation was so far obtained with the satellites SAS-2 (Fichtel et al., 1975) and COS-B (Bignami et al., 1982). In the range 1012-1016 eV detection of the ~,-quanta is performed with ground instruments measuring Cerenkov radiation of extensive air shower (EAS) particles or of charged components of the EAS generated by the primary y-quanta in the atmosphere (see the Review by Vladimirsky et al., 1985). But up to now there have been no 7-ray experiments in the 4-400 GeV energy range, although this interval is of great interest for solving the problem of the origin of the y-radiation.One can describe the energy spectrum of the diffuse gamma-radiation of the Galaxy in the energy range from 0.01 MeV up to 3-4 GeV (for galactic latitudes _+ 10 ~ by the function I(Er) dE~ = AE] n dE 7 with n ~ 1.9 (see Figure 1 and Sacher et al., 1983). According to modern ideas the diffuse y-radiation of the Galaxy at E~ > 0.1 GeV is the result of the decay of n~ generated by primary cosmic-ray protons and nuclei in the process of their interaction with interstellar gas in the galactic disk. In this case the energy spectrum of the 7-radiation must reflect the proton spectrum and consequently have n ~ 2.7. The difference between the observed and expected y-spectrum shapes in the energy range below 4 GeV is possibly connected with the proximity of this energy region to the threshold of n~ formation and the E-27 dependence will occur only at higher energies. That can be discovered if one carries out observations in the energy range 1-400 GeV.It is known that at present about 25 discrete y-sources have been discovered. Their energy spectra are defined only for the most intense sources or for those having some peculiar characteristics. Let us list some data for 4 of them.
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