L. V. Kurnosova

The observation of the galactic anticenter region by the balloon borne gamma-ray telescope Natalya-I

Abstract This paper presents the results of measurements of gamma radiation with energies above 5 MeV, from the galactic anticenter region. The balloon-borne gamma ray telescope “Natalya-I”, was launched on 6 November, 1980 from the Tata Institute of Fundamental Researchs Balloon Facility (Hyderabad, India) and reached ceiling altitude of 35 km. The results on the accelerator calibration of the telescope, using a “tagged” gamma ray beam are also presented.

Geminga pulsar observations with gamma-telescope Gamma-1

Abstract The Geminga light curve obtained with the “Gamma-1” telescope features two peaks separated by 0.5 ± 0.03 period. The light curve is pronounced for γ-quanta energies higher than 400 MeV. The pulsed flux upper limit (1σ) in the energy interval 50 – 300 MeV is 6·10 −7 cm −2 sec −1 . For energies >300 MeV the pulsed component power law spectrum has an exponent 1.1 −0.3 +1.1 and an integral flux (1.1±0.3)·10 −6 cm −2 sec −1 .

Soviet-Indian research of cosmic radiation by high altitude balloons

The report presents some results on the cosmic radiation intensity research carried out with the high-altitude balloons for the period of 1977–1979. The intensity of gamma-radiation with the energy above 40 MeV was measured in two balloon flights at an altitude of 4–7 g/cm2 of residual atmosphere in the vicinity of the geomagnetic equator. A temporal analysis of the intensity to discover fluctuations with periods in the range of 4–60 min was made. Quasi-periodic fluctuations of gamma-radiation intensity with 5 min periods, amplitude ∼20% and duration of several hours were discovered. Possible mechanisms of such fluctuation appearance are discussed. The report gives the results of measuring downward, upward and horizontal electron fluxes in the vicinity of the equator. The obtained data and the data provided by satellites are compared. The report discusses the prospects of further joint Soviet-Indian research of cosmic gamma-radiation.

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′.

The gamma-ray telescope Gamma-1

The telescope ‘Gamma-1’ is designed to investigate cosmic gamma rays in the energy range from 50 MeV to 5000 MeV. The geometrical sensitive area of the telescope amounts to 1500 cm2, the angular resolution in each direction is equal to 1.2° at the energy 300 MeV and is about 20′ when including a coded mask in the telescope, the energy resolution changes from 70% at 100 MeV to 35% at 550 MeV. The characteristics of the telescope and its systems have been determined by the Monte-Carlo method as well as by accelerator calibrations. Discrete sources at the intensity level of 10−7 quanta cm−2 s−1 may be recorded in a year of observations with the gamma-ray telescope ‘Gamma-1’ with a source location accuracy of ≈ 10 arc min.

Gamma-radiation with Eγ > 5 MeV detected from Seyfert galaxy 3C120 and region with 1II = 190° and bII = 20°

Abstract A low mass wire spark chamber gamma ray telescope “Natalya-1” was launched on a balloon flight on November 6, 1980 from Hyderabad, India (Geomagnetic cut-off rigidity R ⋍ 16.8 GV ). The galactic anti-center region was observed during the balloon flight. We report here the detection of gamma rays, with energy, E γ > 5 MeV from the Seyfert galaxy 3C120 and from a region 1II = 190° and bII = 20°. The significance of the detection of gamma rays from 3C120 is also discussed.