The ART-XC telescope on board the SRG observatory

ART-XC (Astronomical Roentgen Telescope - X-ray Concentrator) is the hard X-ray instrument with grazing incidence imaging optics on board the Spektr-Roentgen-Gamma (SRG) observatory. The SRG observatory is the flagship astrophysical mission of the Russian Federal Space Program, which was successively launched into orbit around the second Lagrangian point (L2) of the Earth-Sun system with a Proton rocket from the Baikonur cosmodrome on 13 July 2019. The ART-XC telescope will provide the first ever true imaging all-sky survey performed with grazing incidence optics in the 4-30 keV energy band and will obtain the deepest and sharpest map of the sky in the energy range of 4-12 keV. Observations performed during the early calibration and performance verification phase as well as during the on-going all-sky survey that started on 12 Dec. 2019 have demonstrated that the in-flight characteristics of the ART-XC telescope are very close to expectations based on the results of ground calibrations. Upon completion of its 4-year all-sky survey, ART-XC is expected to detect ~5000 sources (~3000 active galactic nuclei, including heavily obscured ones, several hundred clusters of galaxies, ~1000 cataclysmic variables and other Galactic sources), and to provide a high-quality map of the Galactic background emission in the 4-12 keV energy band. ART-XC is also well suited for discovering transient X-ray sources. In this paper, we describe the telescope, results of its ground calibrations, major aspects of the mission, the in-flight performance of ART-XC and first scientific results.Comment: 19 pages, 30 figures, accepted for publication in Astronomy and Astrophysic

Negative differential conduction in the Bloch oscillations regime in the hexagonal silicon carbide polytypes 4H, 6H and 8H

The paper discusses an experimental demonstration of Bloch oscillations connected with Bragg reflection of electrons from the first miniband edge in superlattices of different silicon carbide polytypes. The original experimental method was geared towards obtaining a strong uniform electric field meeting the conditions of Bloch oscillations. Direct measurements have allowed observation of the negative differential conduction associated with the Bloch oscillations for polytypes 4G, 6H and 8H, having superlattice constants 5, 7.5 and 10 Angstrom respectively. The most recent result is the negative differential conductance for polytype 8H, which is of special interest since it correlates well with the previously obtained data for 4H and 6H polytypes. In fact, the threshold electric fields of negative differential conductance are 290, 150 and 110 kV cm(-1) for polytypes 4H, 6H and 8H respectively. These data, taking into account the difference of the superlattice periods, are in good agreement with the criteria for the Bloch oscillation phenomenon. (C) 1998 Academic Press Limited