A. A. Stepanyan

Observations of the Flux of Very-High-Energy Gamma Rays from the Blazar 3C 66A

Measurements of the flux of very-high-energy (>1 TeV) gamma rays from the blazar 3C 66A obtained over four years are presented. The mean flux over the four-year period was (2.8±0.4)×10−11 cm−2 s−1. There is a correlation between the season-averaged flux of very-high-energy gamma rays and the observed optical radiation.

Observations of the gamma-ray flux from the galaxy Mk 501

We present two-year-long observations of the flux of very-high-energy (∼1012 eV) gamma rays from the active galactic nucleus Mk 501 performed with a Cherenkov detector at the Crimean Astrophysical Observatory. A gamma-ray flux from the object was shown to exist at confidence levels of 11 and 7 standard deviations for 1997 and 1998, respectively. The flux varied over a wide range. The mean flux at energies >1012 eV, as inferred from the 1997 and 1998 data, is (5.0±0.6)×10−11 and (3.7±0.6)×10−11 cm−2 s−1, respectively. The errors are the sum of statistical observational and modeling errors. The mean power released in the form of gamma rays is ∼2×1043 erg s−1 sr−1.

The characteristics of blazars that are sources of very-high-energy gamma rays

We show that the most probable extragalactic sources of very-high-energy gamma rays are HBL blazars whose peak frequencies are in the X-ray. The detection of very-high-energy gamma rays from the blazar 3C66A, which has a redshift of z=0.44, suggests that the density of the intergalactic infrared background at wavelengths >0.6 µm is lower than estimates published in the literature.

A 59-second period in the very high energy gamma-ray emission from the Geminga pulsar

An analysis of our observations of the Geminga object with the GT-48 ground-based gamma-ray telescope has shown that its very-high-energy gamma-ray flux is modulated with a 59-s period. The 59-s period and its time derivative previously inferred from satellite data have been confirmed. According to our data, the period was 61.94 s in 1997 at MSD=50573. The statistical significance of this result is (1−4.5)×10−4.

Ultrahigh-energy gamma-ray emission from the Geminga pulsar

In 1996–1997, the Geminga pulsar was observed at the Crimean Astrophysical Observatory with a ground-based gamma-ray telescope. An analysis of the observational data suggests that this object is a source of ultrahigh-energy 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.

The active galaxy 3C 66A: A variable source of very high-energy gamma-rays

Observations of the very-high-energy gamma-ray flux of the blazar 3C 66A (z=0.444) carried out at the Crimean Astrophysical Observatory with the GT-48 atmospheric Cerenkov detector are reported. The gamma-ray fluxes in 1997 and 1998 were lower than in 1996. The optical luminosity of the object in 1997–1998 also decreased in comparison with its value in 1996. If the emission is isotropic, the very-high-energy gamma-ray power is 1046 erg/s.

Some properties of the radiation of BL Lac objects

Based on the detected positive correlation between the high-energy gamma ray and optical fluxes of the blazars 3C 66A and BL Lac, together with an analysis of spectra of active galactic nuclei from radio to very-high energies, it is proposed that the radio, optical, X-ray, and gamma ray emission, right up to very-high energies, is radiated by a single population of particles—high and very-high energy electrons. These electrons may be associated with the jet that is ejected from the central region of the galaxy at speeds close to the speed of light. The luminosities of the very-high-energy gamma rays of both Galactic and extragalactic objects grow with increasing distance. If the distance increases by an order of magnitude, the luminosity grows by nearly two orders of magnitude, independent of the type of object. The luminosities of gamma ray BL Lac objects at energies higher than 100 MeV grow with distance according to this same law.

Brightness distribution of synchroton radiation in the field of a magnetic dipole and the nature of double radio sources

A model of double radio sources is proposed. In it, the radio radiation is produced by the motion of relativistic particles in a dipole magnetic field whose source is the optical galaxy. Calculations of the apparent brightness distribution of the synchroton radiation of electrons in such a field make it possible to explain some observed features of radio sources: a) the double nature of structure, b) the disposition of the components of the double source on a single straight line with the parent galaxy, c) the dependence of the size of the components on the frequency, d) the preferential direction of the field along the principal axis of the source, e) the similarity of the structures of radio sources in wide ranges of linear and angular sizes. Some other features can also be explained.