V. V. Akimov

Determination of the characteristics of the gamma-ray telescope Gamma-1

The ‘Gamma-1’ telescope has been developed through a collaboration of scientists in the USSR and France in order to conduct γ-ray astronomical observations within the energy range from 50 to 5000 MeV. The major characteristics of the telescope were established by Monte-Carlo simulations and calibrations made with the aid of electron and ‘tagged’ γ-ray beams produced by an accelerator, and these have been found to be as follows: the effective area for photons coming along the instruments axis varies from about 50 cm2 at Eγ = 50 MeV to approximately 230 cm2 at Eγ ≥ 300 MeV; the angular resolution (half opening of the cone embracing 68% events) is equal to 2.7° at Eγ = 100 MeV, and 1.8° at Eγ = 300 MeV; the energy resolution (FWHM) varies from 70% to 35% as the energy of the detected photons increases from 100 to 550 MeV; the telescopes field-of-view at the half-sensitivity level is 300–450 square degrees depending upon the spectrum of the detected radiation, and the event selection logic. Proceeding from the thus obtained characteristics it is demonstrated that a point source producing a photon flux J (Eγ ≥ 100 MeV) = 3 × 10-7 cm-2 s-1, can be detected with a 5σ significance by observing it during 106 s at the level of the Cygnus background, and a source having intensity J (Eγ ≥ 100 MeV) = 10-6 cm-2 s-1 can be detected to within a mean square positional accuracy of about 15′.