Scientific Results

The first observations of EAS in CrAO began in 1970 with the aid of first generation of gamma-ray detectors (RChV-1). It consisted of two pairs of the 1.5 m searchlight mirrors with photomultipliers (PMT) in their focii switched in coincedence circuit. RChV-1 had been working up to 1980 and its data gave some interesting results.

The VHE gamma-ray burst from the Cassiopea direction was detected in 1971. This result was confirmed in 1972. The probable source was named Cas gamma-1. In the same year the VHE gamma-ray burst from the X-ray variable Cyg X-3 has been also detected. The following observations enabled us to find its period. Except the known 4.8 hour period the new 328 days one was found.

During years 1980-1988 and later scientists of the laboratory paid grate attention to the problem of the selection of Cherenkov flashes initiated by VHE gamma-rays. For instance, the Monte-Carlo simulations for cameras with various parameters were performed. Some paper are destined to influence of relatively bright stars on the flash images. The advantage of using two and more telescopes in coincidence was also experimentally investigated.

GT-48 has been working successefully during the few last years. The analysis of the obtained data enabled us to get more interesting results. The observations by GT-48 were began in 1989 but effective operation began in 1993.

The gamma-ray flux from the Crab Nebula was measured in 1993 and 1995. The flux from the Crab Nebula with the energy 1012 eV was detected. According to 1993 year data its value is equal to 2 •10-11 ph/cm2s.

The observations carried out in 1996-1998 permit us to find the gamma-ray flux from a rather distant (z = 0.44) blazar 3C66A with an active nucleus.

The gamma-ray fluxes from Markarian galaxy Mk 501 was also detected. Fig 1. presents the Mk 501 image in gamma-rays according to 1997 year data. We performed calculations of the gamma-ray flux using gamma-ray and p-shower simulations
The flux averaged over the observation time in 1997 at energies E > 1 TeV was found to be (5.0 ± 0.6) · 10-¹¹cm-²s-¹.

In 1998, the flux was (3.7 ± 0.6) · 10-¹¹cm-²s-¹ (the errors are the total statistical observational and modeling errors).

The active galactic nucleus Bl Lac was observed with the GT-48 from July 23 September 1, 1998, in order to search for UHE gamma-ray (>1 TeV) emission. The object was in the field of the detector for more than 24 hours. the source was detected with a high level of confidence, with a flux egual to (2.1 ± 0.4) · 10-¹¹ photons cm-²s-¹.

The Geminga pulsar was observed with a ground- based gamma-ray telescope in 1996-1997. An analysis of the observational data suggests that this object is a source of UHE gamma rays. An analysis of the temporal distribution of gamma-ray photons by an epoch-folding technique reveals a periodicity in the gamma-ray emission with a period of 0.237 s.