Vol 45, No 1 (2019)

The galaxy Mrk 501 has been monitored with the GT-48 Cherenkov telescope at the Crimean Astrophysical Observatory for 14 years (1997–2010). Very-high-energy (VHE) gamma-ray photons have been recorded from Mrk 501 with a total significance of 15σ. The arrival directions of VHE gamma-ray photons have been mapped. They have been identified with Mrk 501. The TeV fluxes from Mrk 501 are shown to be highly variable. The light curves from the data of Cherenkov telescopes and the telescopes that observed Mrk 501 at high energies (MeV and GeV) and in the X-ray and optical bands are presented. Based on the GT-48 observations, we have constructed a TeV spectrum and determined the differential spectral index. The fluxes and spectral characteristics of Mrk 501 inferred from the GT-48 observations are consistent with the data of the MAGIC and H.E.S.S. Collaborations, respectively.

The radio recombination lines (RRLs) of hydrogen, helium (H, He) and carbon (C) have been observed at several positions of the HII region Orion A with the RT-22 radio telescope (Pushchino) at 8 and 13 mm. Information about the ionization structure of the HII region has been obtained. The behavior of y⁺ = n(He⁺)/n(H⁺) over the nebula and model calculations suggest that the effective temperature (Teff) of the star θ¹ C Ori is in the range 35 000–37 500 K, corresponding to a spectral type ≈O6.5 V, which is important for the calibration of hot O-B stars. The electron temperatures (T_e) of this HII region have been measured by taking into account the departures from local thermodynamic equilibrium (LTE); their distribution over the nebula up to distances of 300 arcsec from the center has been derived. The inferred temperatures are in the range 6600–8400 K, strictly decreasing in the eastward directionwith distance from the center, also tend to drop toward the periphery in the southward and westward directions. The turbulent velocities (V_t) of the ionized gas and their distribution over the nebula have been determined. The values of Vt inferred from H RRLs are in the range 9–13 km s⁻¹.

Magnetic quenching of turbulent thermal diffusivity leads to instability of the large-scale field with the production of spatially isolated regions of enhanced field. This conclusion follows from a linear stability analysis in the framework of mean-field magnetohydrodynamics that allows for thermal diffusivity dependence on the magnetic field. The characteristic growth time of the instability is short compared to the 11-year period of solar activity. The characteristic scale of the increased field regions measures in tens of mega-meters. The instability can produce magnetic inhomogeneities whose buoyant rise to the solar surface forms the solar active regions. The magnetic energy of the field concentrations coincides in order of magnitude with the energy of the active regions.