It has been previously demonstrated by Panov et al. (2021) that the TAIGA-HiSCORE Cherenkov array, originally built for cosmic ray physics and ultrahigh-energy gamma-ray astronomy studies using the extensive air shower method, can be used in conventional optical astronomy for wide-field searches for rare nanosecond optical transients of astrophysical origin. The field of view of the facility is on the scale of 1 ster, and it is capable of detecting very rare transients in the visible light range with fluxes greater than approximately 3000 quanta/m2/10 ns (10 ns is the apparatus integration time) and pulse durations of 10 ns. Among the potential sources of distant nanosecond optical transients are the evaporation of primary black holes, magnetic reconnection in the accretion disks of black holes, and signals from distant lasers of extraterrestrial civilizations. The paper describes the methods and results of the search for optical transients using the TAIGA-HiSCORE Cherenkov array from 2018 to 2022 (four winter seasons of data collection). No reliable astrophysical candidates for optical transients were found. We set an upper bound on the flux of the searched events as ∼ 1pt 1 ×10^ - 3 events/ster/h.

The paper presents results of the development and testing with real data of a technology for assessing the emission of nitrogen dioxide and carbon dioxide from sources in Western Siberia. The NO2 content in the region's troposphere was determined using data from the TROPOMI spectroradiometer of the Sentinel-5 Precursor satellite. The method of computational experiments to obtain quantitative estimates of CO2 emissions from large industrial facilities in the region consists in a joint analysis of data from TROPOMI/Sentinel-5P for the NO2 content and data from the OCO-2 orbiting carbon observatory for the CO2 content. The main procedure for data analysis is the approximation of gas content distributions along the trajectory of the OCO-2 satellite by the vector function of the Gaussian distribution. Approximation parameters (full width at half maximum and amplitude), as well as data about direction and speed of wind (obtained from the ERA5 reanalysis) are used to quantify CO2 emissions. The technology developed by the authors for obtaining quantitative estimates of anthropogenic CO2 emissions for the industrial centers of Western Siberia without using OCO-2 data is based on an empirically established relationship between approximation parameters of gases distributions. The results of the work are quantitative estimates of the content of nitrogen dioxide in the atmosphere and lower troposphere of Western Siberia; the annual cycle and interannual variability of NO2 in the troposphere, obtained using data from the TROPOMI/Sentinel-5P spectroradiometer; a technology for obtaining quantitative estimates of CO2 emissions from large industrial centers of the region

Recent experimental data from space-based instruments of the DAMPE and CALET collaborations have shown that the energy spectrum of protons has a new feature, a break in the ∼10 TeV region. In this energy range, the spectrum index of the observed particles varies from - 2.6 to - 2.9. The purpose of this work is to establish the local sources’s position and age that determine this break, the index of the proton generation spectrum in them, as well as the astrophysical interpretation of the results obtained in the DAMPE and CALET experiments. Within the framework of the model of nonclassical diffusion of cosmic rays developed by the authors, which has break due to the propagation of particles in a sharply inhomogeneous (fractal type) galactic medium, it is shown that break in this energy range is formed by tevatron located at a distance of ∼120 pc from the Earth. This source, whose age is ∼5× 105 years, generates particles with a spectrum index ∼2.7 . The power-law behavior of the proton spectrum before and after the break, soft spectrum of particle generation in the source, first obtained in the DAMPE and CALET experiments, should be considered as an indication of the need to revise the standard paradigm accepted today about the sources of cosmic rays, mechanisms of particle acceleration in them and particle propagation in the Galaxy.

The paper discusses an approach that made it possible to estimate the distance to the nearest pevatrons, which form a knee in the spectrum of the cosmic ray nucleon component of about 4 PeV. It is based on the spectra of nucleons and electrons obtained by the authors in the framework of the superdiffusion model of nonclassical cosmic ray diffusion, which have a knee, on the assumption that nucleons and electrons are accelerated by the same type sources and their propagation in an inhomogeneous turbulent galactic medium is characterized by the same diffusion coefficient, and also on the knee in the spectrum of the electronic component in the region of 0.9 TeV, established in the DAMPE experiment. It is shown that pevatrons, which form a knee in the spectrum of the cosmic ray nucleon component of about 4 PeV, are located at distances of the order of 0.75 kpc from the Earth.

Research was carried out on changes in the moisture supply of the territory in the dry steppe subzone of the southern part of Western Siberia (geographic coordinates 50.5°–54.5° N, 77.5°–83.0° E) for the period 1980–2050. The hydrothermal humidification coefficient of G.T. Selyaninov is used as the main indicator of the level of moisture supply in the region. The information basis for this study is the results of six climate models of the CMIP6 family, obtained for the modern period 1980–2015, as well as within the framework of scenarios SSP2-4.5 and SSP5-8.5 of the possible evolution of the global climate system for 2015–2050. The long-term dynamics, boundaries of variations, and trends of the hydrothermal coefficient for the southern part of Western Siberia have been established. An analysis of the influence of the total amount of precipitation and the surface air temperature on the nature and rate of change in the level of moisture supply in the region was carried out. The spatial distribution of moisture supply in the region and the rate of its change for the period under study have been established.

The interannual variability of methane emissions from wetland ecosystems of Western Siberia in 2000–2050 has been investigated. Calculations of CH₄ emission were performed using the approach, in which the total daily methane flux is determined by the sum of positive temperatures accumulated in the soil at that time and its moisture content. Required characteristics of the soil were obtained using regional climate model RegCM4. The reanalysis NCEP-DOE AMIP-II (R2) and data of HadGEM2-ES global model for the RCP4.5 and RCP8.5 evolution scenario of the global climate system were used to define the initial and boundary conditions. It was found that for Western Siberia’s wetland complexes, analyzed in this paper, the model estimates for methane emission in 2000–2013 vary from ~3.5 to ~5.5 Tg CH₄/yr. The average value of emission is 4.34 TgCH₄/yr. The rate of change of methane emission during this period is almost neutral. Growth of CH₄ emission is observed only in the areas of tundra and forest tundra. Forecast values of methane emission obtained for the period 2021–2050 for scenarios RCP4.5 and RCP8.5 ranges from 3.9 up to 7.6 Tg CH₄/yr. The average emission values are 5.0 and 5.8 Tg CH₄/yr, respectively. Trends of CH₄ emission for this period are also practically neutral.

The paper is devoted to the modeling and analysis of data detected by the TAIGA-IACT installation in the stereo mode. Five Imaging Atmospheric Cherenkov Telescopes (IACT) with a viewing angle of 9.6° are expected to be included in the installation. Today there are three telescopes spaced far apart (from 320 to 500 m) in the installation. The effective area of the installation is as large as 0.6 km2; therefore, it is possible to conduct statistically significant measurements of weak γ-ray sources in the energy range above 10 TeV over a reasonable observation time (300–400 h). The Monte Carlo procedure for simulating the hadrons and γ-rays detected by the telescopes is described as is the procedure for reconstructing the parameters of extensive air showers, such as the arrival direction of an event, the axis position, the depth of the maximum of shower development (Xmax), and the primary-particle energy. In order to solve the problem of γ-hadron separation, the criteria for selecting γ-rays detected in the stereo mode have been optimized and the effective area of the installation has been calculated.

In November 2020, the IceCube Neutrino Observatory registered a neutrino event with an energy of 150 TeV directed at the Cygnus Cocoon gamma-ray source. In the Carpet-2 experiment, as part of the Baksan Neutrino Observatory (BNO), a sharp increase in the flow of events with an energy above 300 TeV was recorded from the same direction within the angular accuracy of the events. This flux is 4 orders of magnitude higher than the expected intensity of gamma quanta of this energy region according to data in the region of less than 100 TeV. It was expected that such a powerful flare could be registered by the TAIGA-HiSCORE installation of the TAIGA astrophysical complex. We analyzed the events of the EAS recorded by the installation of TAIGA-HiSCORE for 18 h in October–November 2020 from the Cygnus Cocoon source. This article provides the upper limit of the expected excess flow.

A scintillation experiment is a part of the TAIGA astrophysical complex located in the Tunka Valley, 50 km from Lake Baikal. It consists of the Tunka-Grande and TAIGA-Muon arrays. Its scientific program is devoted to the study of cosmic rays (CRs) and search for astrophysical gamma rays by detecting charged particles (electrons and muons) of extensive air showers (EASs). We present the current status of the scintillation experiment, methods of EAS and CR parameters’ reconstruction, the main results obtained by the Tunka-Grande array and our scientific program for the future.

The TAIGA astrophysical complex includes now 3 IACTs at the distance 300-500 m between each other and 1km2 area wide-angle timing array TAIGA-HiSCORE. At energies above 40 TeV, a hybrid approach to the detection of gamma-rays becomes possible - the detection of EAS by both IACTs and the TAIGA-HiSCORE installation. The main advantage of the joint operation of the IACTs and timing is their good gamma/hadron separation, even by only few telescopes on the large area, by image parameters information and EAS another parameter (core position, direction and energy) that can be better reconstructed by the timing array. In this paper the following topics of a hybrid method are discussed: data processing and analysis, a comparison experimental results with Monte-Carlo simulations, selection of the first events with the energy more than 100 TeV from Crab Nebula in 250 hours of observation. The data were taken during the period of installation deployment, with one IACT in operation and half of the area of TAIGA-HiSCORE installation.

Our study focuses on reconstruction root zone soil moisture (RZSM) in the Kulunda plain, a representative dry steppe area in southern Western Siberia, using remote sensing data (RSD) and machine learning techniques. We employed modern machine learning methods with soil surface layer moisture data from the AMSR2 passive microwave radiometer as the primary predictor. Additionally, we incorporated data from local meteorological and soil hydrological stations, as well as gravity lysimeter data for 2015–2017. This choice of predictors was based on the extensive time series of continuous observations and the availability of selected meteorological parameters. Among the machine learning models we evaluated, Random Forest (RF) and Extreme Gradient Boosting (XGW) yielded the best results, achieving statistical metrics of R-squared (R2) values of 0.96 and 0.94, respectively, with corresponding root mean square error (RMSE) values of 0.34 and 0.41.

This paper is devoted to the analysis of simulation results of TAIGA-IACT in stereo mode of observations and describes the technique of gamma-ray detection with energies higher than several TeV. TAIGA-IACT is part of the TAIGA astrophysics complex. Installation currently consists of three operating telescopes located 300-500 m apart. Two additional telescopes will begin operation in the next two years. We describe a new gamma-hadron separation technique for point-like source observations.

In the era of multi-messenger astronomy it is extremely important to obtain data from many instruments to get the most complete information about transient and short-lasting phenomena. The TAIGA observatory has also started observations in multi-messenger regime. The TAIGA observatory is a hybrid detector complex for high-energy gamma-ray astronomy and cosmic ray physics that combines the detection of extensive air showers with different detector systems: timing array TAIGA-HiSCORE, scintillation array TAIGA-Muon and imaging atmospheric Cherenkov telescopes of the TAIGA-IACT installation. The General Coordinates Network (GCN), that distributes online alerts from different instruments around the world, makes it possible to observe GRBs with TAIGA-IACTs to search for very high energy gamma-quanta. This work presents the current status of the TAIGA-IACT telescope control and alert system for GRB observations as well as its performance.

Experiments on detection of charged particles from EAS in the Tunka Valley are the part of the TAIGA astrophysical complex and consists of two arrays: the operating Tunka-Grande facility and TAIGA-Muon array under construction. In report we present description of arrays, methods of EAS parameters reconstruction, scientific programs and the main results of Tunka-Grande array based on 6 seasons of operation: CR energy spectrum in the energy range 10 PeV - 1000 PeV and limit on the flux of the diffuse gamma rays in the same energy range. In addition, we provide prospects for studying primary cosmic radiation in the energy range 100 TeV - 1000 PeV.

The more correct recalculation from the measured Cherenkov light fluxes at distances of 200 (Q200) and 100 (Q100) m from the Extensive Air Shower (EAS) core to the energy of the primary particle has been developed using the results of M-C simulation by the CORSIKA code, assuming a light primary composition of cosmic rays. Using the new conversion expressions, a differential energy spectrum was obtained according to the data of the Tunka-133 array for 7 years of operation and the TAIGA-HiSCORE array for 2 years of operation.

The status of the TAIGA experiment (Tunka Advanced Instrument for cosmic-ray physics and Gamma-ray Astronomy) located in the Tunka Valley is presented. The paper presents mainly the tasks, developed approaches for their solution, and first results on high-energy gamma-ray astronomy (10 TeV and higher) obtained from a two- to three-year exposure. The current tasks of gamma-ray astronomy and plans for development of the installation are discussed.

A new scenario of the formation of observed ultrahigh-energy cosmic-ray electron/positron and nuclei spectra is discussed within a nonclassical (superdiffusion) model of particle propagation in highly inhomogeneous interstellar and intergalactic media. It is shown that the proposed scenario provides a consistent description of data from highly precise satellite measurements, ground-based hybrid EAS arrays, and Cherenkov telescopes using the spectra of leptons and nuclei, and the mass composition of cosmic rays in the super- and ultrahigh ranges of energy.

The Tunka Advanced Instrument for Gamma-ray and cosmic ray Astrophysics (TAIGA) is a hybrid experiment for the measurement of Extensive Air Showers (EAS) with good spectral resolution in the TeV to PeV energy range. In this domain, the long-sought Pevatrons can be detected. Currently the hybrid TAIGA detector combines two wide angle shower front Cherenkov light sampling timing arrays (HiSCORE and Tunka-133), two 4m class, 10 degrees aperture Imaging Air Cherenkov Telescopes (IACTs) and 240 m(2) surface and underground charged particle detector stations. Our goal is to introduce a new hybrid reconstruction technique, combining the good angular and shower core resolution of HiSCORE with the gamma-hadron separation power of imaging telescopes. This approach allows to maximize the effective area and simultaneously to reach a good gamma-hadron separation at low energies (few TeV). At higher energies, muon detectors are planned to enhance gamma-hadron separation. During the commissioning phase of the first and second IACT, several sources were observed. First detections of known sources with the first telescope show the functionality of the TAIGA IACTs. Here, the status of the TAIGA experiment will be presented, along with first results from the current configuration.

The Tunka-Grande experiment is a scintillation array with about 0.5 km ^2 2 sensitive area at Tunka Valley, Siberia, for measuring charged particles and muons in extensive air showers (EASs). Tunka-Grande is optimized for cosmic ray studies in the energy range 10 PeV to about 1 EeV, where exploring the composition is of fundamental importance for understanding the transition from galactic to extragalactic origin of cosmic rays. This paper attempts to provide a synopsis of the current results of the experiment. In particular, the reconstruction of the all-particle energy spectrum in the range of 10 PeV to 1 EeV based on experimental data from four observation seasons is presented.