The GAMMA-400 gamma-ray telescope is intended to measure the fluxes of gamma-rays and cosmic-ray electrons and positrons in the energy range from 100 MeV to several TeV. Such measurements concern the ...following scientific tasks: investigation of point sources of gamma-rays, studies of the energy spectra of Galactic and extragalactic diffuse emission, studies of gamma-ray bursts and gamma-ray emission from the Sun, as well as high precision measurements of spectra of high-energy electrons and positrons. Also the GAMMA- 400 instrument provides the possibility for protons and nuclei measurements up to knee. But the main goal for the GAMMA-400 mission is to perform a sensitive search for signatures of dark matter particles in high-energy gamma-ray emission. To fulfill these measurements the GAMMA-400 gamma-ray telescope possesses unique physical characteristics in comparison with previous and present experiments. The major advantage of the GAMMA-400 instrument is excellent angular and energy resolution for gamma-rays above 10 GeV. The GAMMA-400 experiment will be installed onboard of the Navigator space platform, manufactured by the NPO Lavochkin Association. The expected orbit will be a highly elliptical orbit (with apogee 300.000 km and perigee 500 km) with 7 days orbital period. An important profit of such an orbit is the fact that the full sky coverage will always be available for gamma ray astronomy.
One of the main objectives of cosmic-ray studies are precise measurements of the energy and chemical composition of particles with extreme energies. Large and sophisticated detectors are used to find ...events seen as showers starting in the Earth's atmosphere with recorded energies larger than 100 EeV. However, a Cosmic-Ray Ensemble (CRE) developing before reaching the Earth as a bunch of correlated particles may spread over larger areas and requires an extended set of detectors to be discovered. The Cosmic-Ray Extremely Distributed Observatory (CREDO) is a solution to find such phenomena. Even simple detectors measuring the particle arrival time only are useful in this approach, as they are sufficient both to provide candidate CRE events and to determine the direction from which they are arriving.
Fermi-LAT has made a significant contribution to the study of high-energy gamma-ray diffuse emission and the observations of 3000 discrete sources. However, one third of all gamma-ray sources (both ...galactic and extragalactic) are unidentified, the data on the diffuse gamma-ray emission should be clarified, and signatures of dark matter particles in the high-energy gamma-ray range are not observed up to now. GAMMA-400, the currently developing gamma-ray telescope, will have angular (∼0.01∘ at 100 GeV) and energy (∼1% at 100 GeV) resolutions in the energy range of 10–1000 GeV which are better than Fermi-LAT (as well as ground gamma-ray telescopes) by a factor of 5–10. It will observe some regions of the Universe (such as the Galactic Center, Fermi Bubbles, Crab, Cygnus, etc.) in a highly elliptic orbit (without shading the telescope by the Earth) continuously for a long time. It will allow us to identify many discrete sources, to clarify the structure of extended sources, to specify the data on the diffuse emission, and to resolve gamma rays from dark matter particles.
The GAMMA-400 experiment: Status and prospects Topchiev, N. P.; Galper, A. M.; Bonvicini, V. ...
Bulletin of the Russian Academy of Sciences. Physics,
03/2015, Volume:
79, Issue:
3
Journal Article
Peer reviewed
The development of the GAMMA-400 γ-ray telescope continues. The GAMMA-400 is designed to measure fluxes of γ-rays and the electron-positron cosmic-ray component possibly associated with annihilation ...or decay of dark matter particles; and to search for and study in detail discrete γ-ray sources, to measure the energy spectra of Galactic and extragalactic diffuse γ-rays, and to study γ-ray bursts and γ-rays from the active Sun. The energy range for measuring γ-rays and electrons (positrons) is from 100 MeV to 3000 GeV. For 100-GeV γ-rays, the γ-ray telescope has an angular resolution of ∼0.01°, an energy resolution of ∼1%, and a proton rejection factor of ∼5 × 10
5
. The GAMMA-400 will be installed onboard the Russian Space Observatory.
The GAMMA-400 telescope will measure the fluxes of gamma rays and cosmic-ray electrons and positrons in the energy range from 100MeV to several TeV. These measurements will allow it to achieve the ...following scientific objectives: search for signatures of dark matter, investigation of gamma-ray point-like and extended sources, study of the energy spectrum of the Galactic and extragalactic diffuse emission, study of gamma-ray bursts and gamma-ray emission from the active Sun, together with high-precision measurements of the high-energy electrons and positrons spectra, protons and nuclei up to the knee.
The bulk of cosmic rays are protons and helium nuclei, whereas the lepton component in the total flux is ∼10−3 at high energy. In the present paper, the simulated capability of the GAMMA-400 telescope to distinguish electrons and positrons from protons in cosmic rays is addressed. The individual contribution to the proton rejection from each detector system of GAMMA-400 is studied separately. The use of the combined information from all detectors allows us to reach a proton rejection of the order of ∼4×105 for vertical incident particles and ∼3×105 for particles with initial inclination of 30° in the electron energy range from 50GeV to 1TeV.
GAMMA-400 γ-ray telescope is designed to measure fluxes of γ-rays and the electron–positron cosmic ray component possibly generated in annihilation or decay of dark matter particles; to search for ...and study in detail discrete γ-ray sources, to examine the energy spectra of Galactic and extragalactic diffuse γ-rays, to study γ-ray bursts and γ-rays from the active Sun. GAMMA-400 consists of plastic scintillation anticoincidence top and lateral detectors, converter-tracker, plastic scintillation detectors for the time-of-flight system (TOF), two-part calorimeter (CC1 and CC2), plastic scintillation lateral detectors of calorimeter, plastic scintillation detectors of calorimeter, and neutron detector. The converter-tracker consists of 13 layers of double (x, y) silicon strip coordinate detectors (pitch of 0.08mm). The first three and final one layers are without tungsten while the middle nine layers are interleaved with nine tungsten conversion foils. The thickness of CC1 and CC2 is 2 X0 (0.1λ0) and 23 X0 (1.1λ0) respectively (where X0 is radiation length and λ0 is nuclear interaction one). The total calorimeter thickness is 25 X0 or 1.2λ0 for vertical incident particles registration and 54 X0 or 2.5λ0 for laterally incident ones.
The energy range for γ-rays and electrons (positrons) registration in the main aperture is from ∼0.1GeV to ∼3.0 TeV. The γ-ray telescope main aperture angular and energy resolutions are respectively ∼0.01 and ∼1% for 102 GeV γ-quanta, the proton rejection factor is ∼5×105. The first three strip layers without tungsten provide the registration of γ-rays down to ∼20 MeV in the main aperture. Also this aperture allows investigating high energy light nuclei fluxes characteristics.
Electrons, positrons, light nuclei and gamma-quanta will also register from the lateral directions due to special aperture configuration. Lateral aperture energy resolution is the same as for main aperture for electrons, positrons, light nuclei and gamma-quanta in energy range E>1.0GeV. But using lateral aperture it is possible to detect low-energy gammas in the ranges 0.2 − 10 MeV and 10 MeV – 1.0GeV with energy resolution 8% − 2% and 2% correspondingly accordingly to GAMMA-400 “Technical Project” stage results. Angular resolution in the lateral aperture provides only for low-energy gamma-quanta from non-stationary events (GRB, solar flares and so on) due segments of CC2 count rate analysis.
GAMMA-400 γ-ray telescope will be installed onboard the Russian Space Observatory GAMMA-400. The lifetime of the space observatory will be at least seven years. The launch of the space observatory is scheduled for the early 2020s.
It has been established that successful repefusion of ocluded infarct-dependent coronary artery (IDCA) during percutaneous coronary intervention does not mean restoration of myocardial perfusion. ...This «no-reflow» phenomenon is known from the studies of R. Kloner, C. Ganote, R. Jennings (1974). They were among the first to note only a partial restoration of coronary blood flow after the reperfusion of mechanically occluded for 90-180 minutes coronary artery in dogs. The authors considered damage to the capillary endothelium, edema of the damaged wall and extravasal tissues, and protrusion into the capillary cavity to be the cause of this phenomenon.
The frequency of the phenomenon of «no-reflow» after the successful restoration of coronary blood flow in the IDCA varies between 5 - 40% of all cases. The development of this phenomenon was an unfavorable prognostic factor, primarily in terms of mortality and deterioration of the functional state of the left ventricle.
The pathophysiology of the «no-reflow» phenomenon remains poorly understood. Obviously, it has a multifactorial nature and cannot be described by any one mechanism.
Analyzing the phenomenon of «no-reflow», it is noted that in spite of the reperfusion of IDCA, there are pronounced pathophysiological changes in the microcirculatory tract, the essence of which is to block myocardial perfusion in the area of myocardial infarction.
During the COVID-19 pandemic, the number of patients with myocardial infarction increased, including an increase in the number of diagnosed «no-reflow» and «slow-flow» phenomena, which is associated with the impact of SARS СOVID-19 virus on the myocardium, namely the development of microvascular damage.
There is currently no specific therapy for the prevention and treatment of «no-reflow» phenomen that would be recommended for patients with STEMI.
This article presents a clinical case of the phenomenon of «no-reflow» in patient B., 56 years old, who complained of severe chest pain, irradiation in the left shoulder and lower jaw, shortness of breath, general weakness. History of hypertension, coronavirus PCR +. Troponin I - 5.4 ng/ml. According to the electrocardiogram: elevation of the ST segment in II. III, aVF leads. At the time of contrast infusion during stenting of infarct-dependent right coronary artery, its slow filling was recorded - the phenomenon of «no-reflow» TIMI 0, MBG-0. The patient was discharged from the hospital in satisfactory condition under the supervision of a family doctor.
Conclusions:
The phenomenon of «no-reflow» is a topical and unresolved issue of myocardial revascularization in real clinical practice.
The most common prerequisite for the development of the phenomenon of «no-reflow» after myocardial revascularization is late hospitalization, and aggravating circumstances - comorbid pathology (COVID-19, hypertension, diabetes).
This clinical case is interesting because the patient with lesions of the lower left ventricular wall PCI was complicated by the phenomenon of «no-reflow», as evidenced by the slowing of ST segment resolution, lack of myocardial perfusion, parietal thrombosis throughout the RCA.
Further search for ways to prevent and treat irreversible blood flow syndrome after successful reperfusion of infarct-dependent coronary artery is needed.
Propagation of ultra-high energy photons in the solar magnetosphere gives rise to cascades comprising thousands of photons. We study the cascade development using Monte Carlo simulations and find ...that the photons in the cascades are spatially extended over millions of kilometers on the plane distant from the Sun by 1 AU. We compare results from simulations which use two models of the solar magnetic field, and show that although signatures of such cascades are different for the models used, for practical detection purpose in the ground-based detectors, they are similar.
Extraterrestrial gamma-ray astronomy is now a source of 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 the angular and energy resolutions. Such a new generation telescope will be GAMMA-400. GAMMA-400, currently developing gamma-ray telescope, together with X-ray telescope will precisely and detailed observe in the energy range of ~20 MeV to ~1000 GeV and 3-30 keV the Galactic plane, especially, 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{\deg} at E{\gamma} = 100 GeV) and energy (~1% at E{\gamma} = 100 GeV) resolutions better than the Fermi-LAT, as well as ground gamma-ray telescopes, by a factor of 5-10. GAMMA-400 will permit to resolve gamma rays from annihilation or decay of dark matter particles, identify many discrete sources (many of which are variable), to clarify the structure of extended sources, to specify the data on the diffuse emission.
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