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The TAIGA observatory addresses ground-based gamma-ray astronomy at energies from a few TeV to several PeV, as well as cosmic ray physics from 100 TeV to several EeV . TAIGA will be located in the Tunka valley, ~ 50 km West from Lake Baikal. The different detectors of the TAIGA will be grouped in 6 arrays to measure Cherenkov and radio emission as well as electron and muon components of atmospheric showers. The combination of the wide angle Cherenkov detectors of the TAIGA-HiSCORE array and the 4-m Imaging Atmospheric Cherenkov Telescopes of the TAIGA-IACT array with their FoV of 10×10 degrees and underground muon detectors offers a very cost effective way to construct a 5 km2 array for gamma-ray astronomy.

The purposes, tasks and design features of the new measuring system of the Cherenkov water detector NEVOD are discussed.

The problem of calibrating a Cherenkov water detector (CWD) and the possibilities for its use based on the example of the CWD NEVOD are discussed. Results of the calibration of quasi-spherical modules in water volume by means of vertical muons selected by scintillation telescopes and compared to the results from measurements performed at test facilities are presented.

A new detecting system of the NEVOD Cherenkov water detector is described, whose development implies replacement of photomultipliers in quasispherical modules of the existing three-dimensional network by low-noise FEU-200 photomultipliers, their dynamic range expansion with the purpose to study events with energies above 1017 eV, the transition to the cluster structure principle, and the possibility of operating in the hodoscopic mode.

A shower array for investigations of primary cosmic rays in the knee region in the energy spectrum of extensive air showers is being designed on the basis of the NEVOD experimental complex. Features of the cluster organization of the array and the results of the study of the characteristics of both the basic scintillation counter and the counter cluster, which is the basic element for triggering, detecting, and data collection and treatment systems, are discussed.

The Cherenkov water detector with volume 2000 m 3 for registration of ν-induced muons from the bottom hemisphere on the ground level was constructed. First results of muon detection are described. Methods of atmospheric muon flux suppression and possibility to reach the rejection factor necessary for separation of ν-induced muons are discussed.

A Cherenkov water detector with volume 9× 9 × 26 cubic meters is described.The spatial lattice of the detector is formed by quasispherical measuring modules which allow to detect Cherenkov light from any direction with practically equal efficiency. Each of the modules consists of six PMTs directed along rectangular coordinate axes. The possibility of neutrino-induced muon detection under conditions of high background on the Earth's surface is discussed. Experimental data obtained during Spring 1996 are analysed.

Data on near-horizontal muons obtained with experimental complex NEVOD-DECOR are analyzed. More than 1.5 × 103 atmospheric muons scattered into upper hemisphere with energy above 7 GeV were registered. Calculations show that the main process forming albedo muon flux near horizon is multiple Coulomb scattering.

The large area coordinate detector (DECOR) represents a multilayer system of plastic streamer tube chamber modules surrounding the Cherenkov water calorimeter NEVOD. Experimental data collected during the test expositions of first. DECOR supermodules (8 vertical planes with 8.4 m 2 working area) have been analysed, angular and spatial reconstruction accuracies have been estimated. The procedure of the selection of events corresponding to detection of parallel tracks (muon bundles originated in the atmosphere) is discussed.

The TAIGA project is aimed at solving the fundamental problems of gamma-ray astronomy and physics of ultrahigh energy cosmic rays with the help of the complex of detectors, located in the Tunka valley (Siberia, Russia). TAIGA includes a wide-angle large area Tunka-HiSCORE array, designed to detect gamma-rays of ultrahigh energies in the range 20 - 1000 TeV and charged cosmic rays with energies of 100 TeV - 100 PeV, large area muon detector to improve the rejection of background EAS protons and nuclei and a network of imaging atmospheric Cherenkov telescopes for gamma radiation detection. We discuss the goals and objectives of the complex features of each detector and the results obtained in the first stage of the HiSCORE installation.

Investigations of the energy characteristics of muon component with the increase of the primary cosmic rays energy can be a key to solving 'muon puzzle' - the problem of excess of EAS muons (observed in several experiments at high - ALEPH, DELPHI - and ultrahigh energies - DECOR, Pierre Auger Observatory) in comparison with the expected flux. The measurements results of the energy deposit of inclined muon bundles in water depending on the zenith angle and the local density of muons are presented. As a measure of the energy deposit, the total number of photoelectrons registered by PMTs of the Cherenkov water calorimeter NEVOD was used. The local density of muons, which gives an estimate of the energy of primary particles was obtained from the data of coordinate-tracking detector DECOR. The experimental data are compared with the results of calculations based on simulations of the muon component of EAS by means of the CORSIKA code.

The analysis of spatial distribution of Cherenkov light generated by cascade showers in Cherenkov water detector (CWD) NEVOD was performed. Showers generated by nearly horizontal muons were selected. Muons tracks were reconstructed with high precision using the coordinate tracking detector DECOR. For the first time, the dependence of Cherenkov light intensity on the depth of a shower at different distances from its axis was measured.

The problem of high energy neutrino detection on the Earth's surface is discussed. The first results of experimental study of ν-induced muons in Cherenkov water detector on the ground level are considered.

Quasispherical Module (QSM) of Cherenkov water detector NEVOD represents six low-noise FEU-200 photomultipliers with flat photocathodes (15 cm in diameter), oriented along the axes of orthogonal coordinate system. Such configuration allows to register Cherenkov radiation arriving from any direction with almost equal efficiency. The results of measurements of QSM characteristics in the sensitive volume of the NEVOD detector during the registration of Cherenkov radiation of single muons at different distances and angles are discussed.

First results of investigations of the energy deposits of inclined muon bundles in the ground-based Cherenkov water detector NEVOD are presented. As a measure of the muon bundle energy deposit, the total number of photoelectrons detected by PMTs of the Cherenkov calorimeter is used. For each event, the local muon density at the observation point and the muon bundle arrival direction are estimated from the data of the coordinate-tracking detector DECOR. Registration of the bundles in a wide range of zenith angles allows to explore the interval of primary particle energies from ̃ 1016 to ̃ 1018 eV. Measurement results are compared with CORSIKA based simulations of EAS muon component. It is found that the mean energy of muons detected in the bundles rapidly increases with the zenith angle and reaches about 500 GeV near the horizon.

In several cosmic ray experiments, an excess of multi-muon events in comparison with calculations performed in frame of the widely used hadron interaction models was found. In order to solve this puzzle, investigations of muon energy characteristics in EAS are required. An experiment on the measurement of the energy deposit of muon bundles in water has been started with the NEVOD-DECOR experimental complex. The results of the analysis of the first experimental data are discussed. It has been found that the average specific energy deposit in the Cherenkov calorimeter appreciably increases with zenith angle, thus reflecting the increase of the mean muon energy in the bundles. A possible evidence for an increase of the energy deposit at primary energies above 10 17 eV is observed.

TAIGA stands for ``Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy'' and is a project to built a complex, hybrid detector system for ground-based gamma-ray astronomy from a few TeV to several PeV, and for cosmic ray studies from 100 TeV to 1 EeV. TAIGA will search for ``PeVatrons'' (ultra-high energy gamma-ray sources) and measure the composition and spectrum of cosmic rays in the knee region (100 TeV–10 PeV) with good energy resolution and high statistics. TAIGA will include Tunka-HiSCORE — an array of wide-angle air Cherenkov stations, an array of Imaging Atmospheric Cherenkov Telescopes, an array of particle detectors, both on the surface and underground and the TUNKA-133 air Cherenkov array.

Russian-Italian NEVOD-DECOR experiment on the measurements of the local muon density spectra (LMDS) at various zenith angles gave possibility to obtain information on primary cosmic ray flux and interaction characteristics in a record wide energy range from 1015 to more than 1018 eV. Comparison of the measurement results with CORSIKA-based simulations showed the increase of LMDS slope at PeV energies of primaries (corresponding to the first knee); a trend to a heavier primary mass composition above the knee; indication for a second knee (a further increase of the spectrum slope near 1017 eV). At large zenith angles and high muon densities (corresponding to primary energies around 1018 eV) a considerable excess of muon bundle events in comparison with the expectation based on independent estimates of the primary spectrum and widely used hadron interaction models has been found. In 2011, a new phase of measurements of the energy spectrum of cascade showers initiated by high-energy muons in water and of the energy deposit of muon bundles at various zenith angles and muon multiplicities started. Further plans include the deployment of a traditional EAS array around the NEVOD-DECOR complex.

The technique of cascade shower energy measurements by means of Cherenkov water detector (CWD) NEVOD with a spatial lattice of quasi-spherical modules (QSM) is discussed. A dense QSM spacing allows to reconstruct the number of cascade particles along the shower axis on the basis of amplitude responses of PMTs. The technique of cascade curve reconstruction was applied to showers generated in water by nearly horizontal high energy muons selected by means of the coordinate detector DECOR deployed around the CWD. First results of cascade energy spectrum measurements are presented.

New setup for detection of EAS electromagnetic component at the knee region of primary energies is under construction on the basis of the experimental complex NEVOD (Moscow, Russia). The measuring system of the EAS array has a cluster organization. Clusters are located on the roofs of laboratory buildings of MEPhI (Moscow). Features of measuring and DAQ systems, results of investigations of characteristics of a single counter and the event formation algorithm from the data of separate clusters are discussed.

The use of quasi-spherical modules with several PMTs with flat photocathodes in Cherenkov water detectors is discussed. Properties of the response of such modules are examined. The characteristics of the quasi-spherical module with six PMTs that is used in the Cherenkov water calorimeter NEVOD are considered. The results of studying the isotropy of the amplitude response of this module and the quality of reconstruction of light direction with a single module and with a group of modules are demonstrated.

Imaging Atmospheric Cherenkov Telescopes (IACTs) are one of the key parts of the TAIGA observatory, which is designed to study gamma rays and charged cosmic rays in the energy range of 10^13 eV – 10^18 eV. The current prototype phase comprises three IACTs. The first IACT was fabricated at JINR, Dubna, and started its first commissioning season in the Tunka valley in 2017. The second one has been assembled there in fall 2018, the third structure one is ready for installation in autumn 2019. This report presents the main TAIGA IACT characteristics and results from pointing performance studies in the last 2 seasons. We also describe R&D activities started to fabricate focusing glass mirrors at JINR, and give results for the first prototypes measurements.

The first IACT as part of the gamma and cosmic-ray experiment TAIGA was installed in the Tunka Valley near Lake Baikal in fall 2016. In the following months different systems of the telescope were put into test operation. We started the commissioning phase of operating the telescope in time coincidence with the wide angle integrating air Cherenkov HiSCORE array, which for the time being comprises 28 working stations. We anticipate that the hybrid operation of the non-imaging and imaging telescopes will lead to a cost-efficient, highly sensitive detector operating in the energy range from 30-50 TeV till several PeV. Here we want to report on the first test results of operating the prototype hybrid array. We will focus on the analysis of count rates and image size spectra for all events detected by the IACT and the joint events detected also by the HiSCORE array, comparing these with expectations from MC simulations.

The TAIGA (Tunka Advanced Instrument for cosmic rays and Gamma-Astronomy) observatory is designed to study the gamma ray sources and galactic cosmic rays. It is located in the Tunka Valley 50 km from the lake Baikal (Siberia). The first part of TAIGA called the EAS Cherenkov array TAIGA-HiSCORE currently consists of 28 wide-angle (0.6 sr) stations, distributed over an area of 0.25 km^2. The Crab observation exposure was about 115 hours during the winter seasons of 2016-2017. The expected gamma quanta excess depends on the array energy threshold and a model of the Crab energy spectrum extrapolation to the higher energies. We present preliminary results of experimental data and MC simulations comparison as well as energy threshold and angular resolutions. The experimental data is in a good agreement with the simulations. An excess of events (about 25 events in the region 30-63 TeV) observed from the Crab direction is compatible with the expected one.

The first imaging atmospheric Cherenkov telescope as a part of the TAIGA (Tunka Advanced Instrument for cosmic rays and Gamma Astronomy) detector was put into commission in the Tunka valley in December 2016. The reflector of the telescope follows the Davis-Cotton design. It is composed of 34 glassmirror tiles, each of 60 cm diameter, and has a diameter of 4.3 m. The focal length is 4.75 m. The imaging camera includes 560 photomultiplier-based pixels, providing a FoV of ~10×10 degrees. The imaging camera is made by using a modular principle and includes trigger, data acquisition and processing systems based on MAROC3 chips. The slow control system monitors the count rate and the PMT anode currents as well as controls the high voltage. For monitoring performance of the camera a dedicated calibration system based on nanosecond pulsed LED light source was developed.