Yu. I. Neshpor

Using the trial source method for the analysis of the influence of apparatus errors on data obtained by the VHE imaging cerenkov detectors

The results of application of the trial source method for the analysis of data obtained using a VHE gamma-ray telescope with an imaging camera are presented. This method was proposed by the Whipple Collaboration in 1991. The usage of this method gives us the possibility of the more accurate determination of the direction to the source. In consequence, more accurate definition of the source direction helps us to make more confident identification of the VHE gamma-ray source and to find more accurate value of the gamma-ray flux.The three-dimensional histograms show that the position of an off-axis source is shifted towards the camera edge and the height of the peak (i.e.the efficiency of the detection) decreases in this case.The calculated histograms obtained for the case of a bright star in the camera field of view show that a spurious source appears in the direction of the star. The trial source method gives us the possibility of distinguishing the real gamma-ray source from a spurious one.

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.

Observations of active galactic nuclei with the GT-48 CrAO gamma-ray telescope in 2004

Observations of several active galactic nuclei were performed with the GT-48 gamma-ray telescope at CrAO in 2004: 3C 66A, Mk 421, Mk 501, 1H 1426, 1ES 1959, and BL Lac. Very-high-energy (E ≥ 1012 eV) gamma-ray fluxes were recorded from 3C 66A, Mk 421, Mk 501, and 1H 1426 at a confidence level of more than 4σ. Upper limits for the flux of very-high-energy gamma rays are presented for 1ES 1959 and BL Lac. The 2004 observational data for 3C 66A (z = 0.44) confirm the results obtained previously at CrAO.

Results of observation of Cyg γ-2, BL Lac, 3C66A, Mk 501, and the Crab nebula by the GT-48 gamma-ray telescope in 2006

The active galactic nuclei BL Lac, 3C66A, and Mk501, as well as the Crab nebula and the Cyg γ-2 source were observed in 2006 at the Crimean Astrophysical Observatory using the GT-48 gamma-ray telescope. Very high energy (VHE) gamma-ray fluxes at a high confidence level (Q > 4) were detected from the active galactic nuclei and the Crab nebula. VHE gamma-ray fluxes from the unidentified gamma-ray source Cyg γ-2 and the X-ray source Cyg X-3 were recorded during observations of Cyg γ-2.

Observations of the gamma-ray flux from the X-ray source Cyg X-3 in 1994–1995

We present the observations of Cygnus X-3 carried out with the GT-48 gamma-ray telescope at the Crimean Astrophysical Observatory in 1994–1995. The mean gamma-ray flux at energy E>1012 eV is shown to be approximately equal to 1.3×10−11 cm−2 s−1. The flux in 1994 was much lower than that in 1995, being (6.2±2.6)×10−12 cm−2 s−1; i.e., it was statistically insignificant. The flux in 1995 was (2.7±0.7)×10−11 cm−2 s−1. Thus, the very high energy gamma-ray emission from Cyg X-3 is variable. These measurement results can be used to obtain upper limits on the flux from Cyg X-3 in 1994–1995.

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.

Particular features of γ radiation from active galactic nuclei

The luminosity of γ radiation from active galactic nuclei is shown to grow with increasing distance to the object. Absorbance of very high-energy γ quanta is far less than the values published so far. High-energy particles are accelerated more effectively when the galactic radiation is enhanced.

Long-term observations of galaxy 3C 66A

Monitoring of the active galaxy nucleus 3C 66A in the VHE γ-ray and analysis of data in X-rays and optical ranges over the period 1996–2009 were carried out. The nature of processes responsible for one or another type of radiation appeared to be very complicated since, at certain periods of time, an either positive or negative correlation may be observed between different types of radiation. Period of radiation P = 365 days in the X-ray range was found.

Variability of radiation from the Crab Nebula

We consider variations of the radiation from the Crab Nebula in two energy ranges: X-rays (2–10 keV) and very-high-energy (>1 TeV) gamma rays. We demonstrate the presence of sine-shaped quasi-periodic variations in the X-ray range, with the period P = 862 d. A positive correlation was detected between variations of X-rays and gamma rays (the HEGRA data) with time.

The efficiency of light guide application in imaging cameras of the 2-nd generation gamma-ray Cherenkov telescopes

The light collection efficiency of conical focons was measured as a function of the incident angle of light. The results show that the application of focons in imaging cameras of gamma-ray telescopes may increase the utilization factor of the light up to 1.7 times.