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Extraterrestrial gamma-ray astronomy is now a source of a new knowledge in the fields of astrophysics, cosmic-ray physics, and the nature of dark matter. The next absolutely necessary step in the development of extraterrestrial high-energy gamma-ray astronomy is the improvement of the physical and technical characteristics of gamma-ray telescopes, especially their angular and energy resolutions. Such a new generation telescope will be GAMMA-400, currently under development. Together with an X-ray telescope, it will perform precise and detailed observations in the energy range of ~20 MeV to ~10 000 GeV and 3–30 keV the Galactic plane, especially, toward the Galactic Center, Fermi Bubbles, Crab, Cygnus, etc. The GAMMA-400 will operate in the highly elliptic orbit continuously for a long time with the unprecedented angular (~0.01◦ at Eγ = 100 GeV) and energy (~1% at Eγ = 100 GeV) resolutions, exceeding the Fermi-LAT as well as ground-based gamma-ray telescopes by a factor of 5–10. GAMMA-400 will permit resolving gamma rays from annihilation or decay of dark matter particles, identifyingmany discrete sources (many of which are variable), clarifying the structure of extended sources, specifying the data on the diffuse emission, as well as measuring electron + positron fluxes and specifying electron + positron spectrum in the energy range from 1 GeV to 10 000 GeV.

The design is described and the main measurement results are reported for a prototype of a high-energy event registration system of a gamma-ray space telescope on the positron beam of the S‑25R Pakhra synchrotron, Lebedev Physical Institute of the Russian Academy of Sciences. The prototype includes anticoincidence and time-of-flight systems, a pre-shower detector, and a calorimeter based on BC-408, BGO, and CsI(Tl) scintillators with the corresponding front-end and processing electronics units. Silicon photomultiplier matrices are used as photo sensors of all scintillation detectors of the prototype.

The space-based gamma-ray telescope must effectively separate photons from charged particles of instrumental background and cosmic rays. It requires that the anticoincidence system of the telescope must have high detection efficiency, large dynamic range and good enough energy and time resolution for charged particles. The main results obtained using 246 MeV secondary positron beam of synchrotron S-25R “PAKHRA” of Lebedev Physical Institute with prototype of system of anticoincidence detectors of space-based gamma-ray telescope GAMMA-400 are presented. The amplitude resolution, time resolution and charged particles detection efficiency are adduced. All measurements were performed using “fast” output of silicon photomultipliers of prototype scintillation detectors sensors. Fractal dimensions of temporal profiles registered during measurements using positron beam and atmospheric muons are discussed.

The space observatory GAMMA-400 is processed currently in accordance with the Federal Space Program of the Russian Federation for 2016–2025. The observatory includes a gamma-ray telescope for experimental studies of gamma rays in the energy range from ~20 MeV to ~1 TeV with high angular and energy resolution, as well as for research of electrons + positrons at energies above 100 GeV in both the main (top-down), and lateral apertures. At present time, there are experimental indications concerning the possibility of existing of spectrum break in electrons + positrons intensities about TeV energies. This point stimulates several speculations to explain such phenomena. In this paper we examined capabilities of GAMMA-400 telescope to explore this problem. The methods for electron detection in the energy range from 100 GeV up to 10 TeV from the lateral aperture of a gamma-ray telescope are presented. Also, the results of calculation for proton rejection factor and for electron acceptance are revealed.

AbstractThe future space-based γ-ray telescope GAMMA-400 will be installed on the Navigator platform of the Russian astrophysical observatory. A highly elliptical orbit will allow prolonged (~100 days) continuous observations of many regions of the celestial sphere for 7–10 years. GAMMA-400 will measure fluxes of γ‑ray emission in the energy range of ~20 MeV to several TeV and electrons + positrons to ~20 TeV. The γ-ray telescope will have excellent separation of γ-ray emissions against the background of cosmic rays and electrons + positrons from protons, along with unprecedented angular (~0.01° at Eγ = 100 GeV) and energy (~1% at Eγ = 100 GeV) resolutions 5–10 times better than for the Fermi-LAT and ground-based γ-ray telescopes. GAMMA-400 observations will provide fundamentally new data on discrete sources and spectra of γ-ray emissions and electrons + positrons.

AbstractThe GAMMA-400 space project is one of the new generation of space observatories designed to search for signs of dark matter in the cosmic gamma emission, and to measure the characteristics of diffuse gamma-ray emission and gamma-rays from the Sun during periods of solar activity; gamma-ray bursts; extended and point gamma-ray sources; and electron, positron, and cosmic-ray nuclei fluxes with energies in the TeV ranges. The GAMMA-400 γ-ray telescope constitutes the core of the scientific instrumentation. The nature of the intended experiments imposes stringent requirements on the gamma telescope’s system of trigger signal formation, now being developed using the state-of-the-art logic devices and fast data links. The design concept of the system is discussed, along with the chosen engineering solutions and some experimental results obtained during the operation of the system prototype using a positron beam with energies of 100–300 MeV from the PAKHRA S-25R synchrotron at the Lebedev Physical Institute.

AbstractThe PAMELA magnetic spectrometer was launched onboard the Resurs-DK1 satellite into a near-polar Earth orbit with an altitude of 350–600 km, in order to study fluxes of cosmic ray particles and antiparticles in the wide energy range of ~80 MeV to hundreds of GeV. The results from observations of electron and positron fluxes in 2006–2016 are presented.

The task of selecting neutral γ rays from the background of charged particle fluxes, which arises in investigation of high-energy (>50 GeV) cosmic rays, is complicated by the presence of the backsplash effect. The backsplash is composed of a great number of low-energy (~1 MeV) particles produced in an electromagnetic shower being developed in the calorimeter of the γ-ray telescope. A technique of charged particle rejection using an anticoincidence system has been developed. A method for discriminating events of charged particle detection from γ-ray detection events accompanied by the backsplash phenomenon is proposed. This method is based on the difference of the signals in time and makes it possible to maintain a high detection efficiency even for high-energy γ rays.

The characteristics of the prototype of the scintillation detecting segment of time-of-flight and anticoincidence systems of being developed space-based GAMMA-400 gamma-ray telescope is studied. The amplitude resolution, time resolution and charged particle detection efficiency of the prototype with silicon photomultipliers readout obtained using 250 MeV positron beam of synchrotron C-25P ‘‘PAKHRA’’ of P.N. Lebedev Physical Institute are presented. The comparison of applying both ‘‘standard’’ and ‘‘fast’’ outputs of silicon photomultipliers type ON Semiconductor MICROFC-60035-SMT used in the prototype is featured.

The GAMMA-400 gamma-ray telescope is the successor of Soviet and Russian gamma-ray telescopes. GAMMA-400 is being developed for cosmophysical research in accordance with the Russian Federal Space Program 2016–2025. The GAMMA-400 experiment will be implemented aboard the Russian astrophysical space observatory in a highly elliptic orbit during 7 years to provide new data on gamma-ray emission mainly from the Galactic plane, Galactic Center, the Sun and cosmic-ray electron positron fluxes. The main mode of observations will be the continuous point-source mode with the duration of up to 100 days. The GAMMA-400 gamma-ray telescope will study high-energy gamma-ray emission up to several TeV and cosmic-ray electrons positrons up to 20 TeV. GAMMA-400 will have the never-achieved angular resolution, the high-energy and time resolutions, as well as very good separation efficiency of gamma rays from cosmic-ray background and of electrons positrons from protons. The distinctive features of GAMMA-400 are the excellent angular resolution of at GeV that exceeds resolutions of the space-based and ground-based gamma-ray telescopes by a factor of 5–10, as well as high-energy resolution of at GeV. GAMMA-400 studies can discover gamma-ray emission from annihilation or decay of dark matter particles, identify many unassociated discrete sources, explore the structure of extended sources, search for gamma-ray bursts and solar gamma-ray flares, improve the data on cosmic-ray electron positron spectra for energies of >50 GeV.