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

Abstract

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 instrument's axis varies from about 50 cm² at E _γ = 50 MeV to approximately 230 cm² at E _γ ≥ 300 MeV; the angular resolution (half opening of the cone embracing 68% events) is equal to 2.7° at E _γ = 100 MeV, and 1.8° at E _γ = 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 telescope's 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 (E _γ ≥ 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 (E _γ ≥ 100 MeV) = 10^-6 cm^-2 s^-1 can be detected to within a mean square positional accuracy of about 15′.