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The Tunka Advanced Instrument for Gamma- and cosmic-ray Astronomy (TAIGA) is a multicomponent experiment for the measurement of TeV to PeV gamma- and cosmic rays. Our goal is to establish a novel hybrid direct air shower technique, sufficient to access the energy domain of the long-sought Pevatrons. The hybrid air Cherenkov light detection technique combines the strengths of the HiSCORE shower front sampling array, and two ∼4 m class, ∼9.6° field of view Imaging Air Cherenkov Telescopes (IACTs). The HiSCORE array provides good angular and shower core position resolution, while the IACTs provide the image shape and orientation for gamma-hadron separation. In future, an additional muon detector will be used for hadron tagging at ≥100 TeV energies. Here, only data from the first IACT of the TAIGA experiment are used. A randomforest algorithm was trained using Monte Carlo (MC) simulations and real data, and applied to |$85\, \mathrm{h}$| of selected observational data tracking the Crab Nebula at a mean zenith angle of 33.5°, resulting in a threshold energy of 6 TeV for this data set. The analysis was performed using the gammapy package. A total of 163.5 excess events were detected, with a statistical significance of 8.5 σ. The observed spectrum of the Crab Nebula is best fit with a power law above 6 TeV with a flux normalization of (3.20 ± 0.42) · 10−10 TeV−1 cm−2 s−1at a reference energy of |$13\, \mathrm{TeV}$| and a spectral index of −2.74 ± 0.16. [ABSTRACT FROM AUTHOR]

A study is made of the astroclimatic conditions for performing nighttime astrophysical observations on the territory of the Greater Altai region. Nighttime data from both the VIIRS radiometer of the Suomi NPP satellite platform and the AIRS hyperspectrometer of the Aqua satellite are used. Topographic and astroclimatic criteria show that the Chuya steppe region (Altai Republic, Russia) and the plateau of Lake Khubsugul (Aimak Khuvsgel, Mongolia) are best suited for the deployment a full-scale gamma astronomy experiment. Infrastructure considerations make the territory in the western part of the Chuya steppe preferable. [ABSTRACT FROM AUTHOR]

The TAIGA hybrid gamma-ray observatory is currently being developed in the Tunka Valley, 50 km from Lake Baikal, to study gamma radiation and charged cosmic ray fluxes in the 1013–1018 eV range. The first results are presented for detecting gamma rays from the Crab Nebula in 44 h of observation, and from the blazar Markarian 421 in 62 h of observation with a significance of around 5–6 σ by one of the TAIGA IACT telescopes. [ABSTRACT FROM AUTHOR]

The prototype of a small wide-angle telescope was installed within the astrophysical complex TAIGA in the Tunka Valley in September 2019. Data were collected on the prototype's performance during the last eight observation sessions. Operating regimes of the telescope's systems, the trigger system, and the system for synchronizing with the TAIGA complex were tested. The first results from analyzing data on the prototype telescope's performance are presented. [ABSTRACT FROM AUTHOR]

The astrophysical complex TAIGA (Tunka Advanced Instrument for cosmic-ray physics and Gamma-ray Astronomy), whose first phase is being completed in the Tunka valley 50 km from Lake Baikal, is described. Its research program, first results, and development prospects are discussed. [ABSTRACT FROM AUTHOR]

The Tunka-133 Cherenkov complex for recording extensive air showers (EAS) collected data over seven winters from 2009 to 2017. The differential energy spectra of all particles was acquired in the 6 × 1015–3 × 1018 eV range of energies over 2175 h. The TAIGA-HiSCORE complex is continually being expanded and upgraded. Data acquired by 30 first-line stations over 35 days during the period 2017–2018 is analyzed in this work. As at the Tunka-133 setup, the primary particle energies above 1015 eV are measured using the density of the Cherenkov light flux at a distance of 200 m from a shower's axis. Data on lower energies are collected by determining the energy of the light flux near a shower's axis. This results in a spectrum of 2 × 1014–1017 eV. The combined spectrum for the two systems covers a range of 2 × 1014–2 × 1018 eV. [ABSTRACT FROM AUTHOR]

The relevance and benefits of the new TAIGA gamma observatory complex in the Tunka Valley (50 km from Lake Baikal) are discussed. The main aim of the TAIGA installation is to study high-energy gamma radiation and search for cosmic pevatrons. The first series of gamma stations was commissioned in 2019 and covers an area of 1 km2. Its expected integral gamma radiation sensitivity at an energy of 100 TeV over 300 h of source monitoring is (2–5) × 10−13 TeV cm−2 s−1. It is planned to expand the effective area of TAIGA gamma observation to 10 km2 in the future. [ABSTRACT FROM AUTHOR]

A corrected energy dependence of the depth of the maximum in the wide range of energies 1015 to 1018 eV is obtained using data collected at the Tunka-133 facility over 7 years of operation (2009–2017) and the TAIGA-HiSCORE facility in the 2019–2020 season. At the highest energies, our results match those of the Pierre Auger observatory. The results are converted to parameter ❬ln A❭, which characterizes the mean EAS composition. [ABSTRACT FROM AUTHOR]

A new knee-like approximation of the lateral distribution function (LDF) of EAS Cherenkov light in the 30-3000 TeV energy range was proposed and tested with simulated showers in our earlier studies. This approximation fits the LDFs of individual showers accurately for all types of primary particles gamma-rays, protons, and nuclei) and is suitable for reconstructing the shower core, determining the energy, and separating gamma-induced showers from hadron-induced ones. In the present study, the knee-like fitting function is used to determine the parameters of real showers detected by TAIGA-HiSCORE. It is demonstrated that this approximation characterizes properly all types of individual LDFs of experimental events in the 300-1000 TeV range. The accuracy of fit is governed by fluctuations intrinsic to the process of measurement of the Cherenkov photon density. The probability density function of these fluctuations was reconstructed and introduced into simulations. Certain useful methodical applications of the knee-like approximation are con-sidered, and the possibility of shower sorting into nuclei groups is examined. The extensive statistical coverage and detailed LDF measurement data of HiSCORE have provided the first opportunity to examine in depth the LDF of Cherenkov radiation in the 300-1000 TeV range. [ABSTRACT FROM AUTHOR]

Over the past few years, the TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma-ray Astronomy) observatory has been being deployed in the Tunka Valley, Republic of Buryatia. It is designed for studying gamma rays of energy above 30 TeV and performing searches for sources of galactic cosmic rays with energies in the vicinity of 1 PeV, which is an energy region around the classic knee in the cosmic-ray energy spectrum. The first phase of the observatory will be situated at a distance of about 50 km from Lake Baikal at the site of the Tunka-133 array. The TAIGA gamma observatory will include a network of 500 wide-angle (0.6 sr) Cherenkov detectors (TAIGA-HiSCORE array) and up to 16 atmospheric Cherenkov telescopes (ACT) designed for analyzing the EAS images (imaging atmospheric Cherenkov telescopes, or IACT) and positioned within an area of 5 km2. The observatory will also include muon detectors of total area 2000 m2 distributed over an area of 1 km2. Within the next three years, it is planned to enhance the area of the TAIGA-HiSCORE array by a factor of four—from 0.25 km2 to 1 km2; to supplement the existing IACT with two new ones; and to deploy new muon detectors with a total coverage of 200 m2. The structure of the new observatory is described along with the data analysis techniques used. The most interesting physical results are presented, and the research program for the future is discussed. [ABSTRACT FROM AUTHOR]

The design for the TAIGA-HiSCORE array, a part of the TAIGA Gamma Ray Observatory, is considered. The observatory is being constructed in the Tunka Valley, 50 km from Lake Baikal. Preliminary results obtained using the first 28 optical stations of the array are presented. [ABSTRACT FROM AUTHOR]

The Tunka-HISCORE wide-angle Cherenkov array, one part of the planned TAIGA integrated gamma observatory intended for investigations in the field of high-energy (>30 TeV) gamma-ray astronomy and cosmic-ray physics, is deployed in the Tunka Valley (Buryat Republic). The first results from operating a prototype array composed of nine stations spread over an area of ∼0.1 square kilometers during the winter of 2013-2014 are presented. Data processing techniques are described, along with data on the accuracy of reconstructing the position of a shower's axis, energy, and angle of arrival. The differential spectrum of all cosmic-ray particles in a shower in the energy range of 2 × 10 to 2 × 10 eV is presented and compared to the available data. [ABSTRACT FROM AUTHOR]

The Tunka Radio Extention (Tunka-Rex) is an array of radio antennas located at the TAIGA (Tunka Advanced Instrument for Cosmic Ray Physics and Gamma Astronomy) facility. The array occupies an area of approximately 3 km and contains 63 antennas. The results from the first two seasons of Tunka-Rex operation (2012-2014) and antenna array modernization (2015-2016) are presented. [ABSTRACT FROM AUTHOR]

We present the results of our search for neutrino events coinciding in time and direction with gamma-ray bursts (GRBs) with the Baikal underwater neutrino telescope NT200. No events confirming a neutrino accompaniment of GRBs have been detected. Model-independent limits (Greens function) on the neutrino flux from GRBs have been obtained. For the Waxman-Bahcall neutrino spectrum, the limit on the neutrino flux from a GRB has been found to be EΦ ⩽ 1.1 × 10 GeV cm s sr. [ABSTRACT FROM AUTHOR]

A project of the NT1000 deep-water neutrino telescope with an effective volume of ∼1 km is currently being developed by the BAIKAL collaboration. The telescope will be located in Lake Baikal in close vicinity of the NT200+ detector, which is currently in operation. The telescope will be composed of 12 clusters with 8 similar strings of optical modules in each (each string has two sections of the NT1000 optical modules). The section of the NT1000 optical modules has been developed using higher-efficiency photomultiplier tubes and state-of-the-art electronics. The field tests of the experimental string consisting of two sections with six optical modules in each have been performed. The results of these investigations are used in the project of the NT1000 neutrino telescope and in the hydrological study of Lake Baikal. [ABSTRACT FROM AUTHOR]

A new analysis of the data from the NT200 neutrino telescope based on the reconstruction of parameters for high-energy showers generated in neutrino interactions has yielded new upper limits on the diffuse neutrino fluxes predicted by a number of theoreticalmodels. The upper limit on the all-flavor neutrino flux with an energy spectrum E−2 is E2Φ ν < 2.9 × 10−7 GeV cm−2 s−1 sr−1. [ABSTRACT FROM AUTHOR]

High-frequency noise of Lake Baikal is investigated using a submersible self-contained instrument to determine the noise background for the acoustic detection of superhigh-energy neutrinos. It is found that, under stationary and uniform meteorological conditions, the integral noise power in the frequency band 1–50 kHz is virtually independent of depth and is 10–200 mPa or more, depending on the specific conditions. The noise itself contains multiple short pulses of different amplitudes and shapes. [ABSTRACT FROM AUTHOR]

Results of calibration of the PAMELA instrument at the CERN facilities are discussed. In September, 2003, the calibration of the Neutron Detector together with the Calorimeter was performed with the CERN beams of electrons and protons with energies of 20 – 180 GeV. The implementation of the Neutron Detector increases a rejection factor of hadrons from electrons about ten times. The results of calibration are in agreement with calculations. [ABSTRACT FROM AUTHOR]

The hydroacoustic coordinate-measuring system of the NT-200 Baikal neutrino telescope is described. It is a ranging long-base hydroacoustic system constantly operating in an automated or interactive mode and capable of measuring the coordinates of the detecting modules of the NT-200 to within 20 cm. Special attention is given to the justification of the estimate of the coordinate measurement errors. As an illustration, some results of measuring the coordinates of the elements of the NT-200 and the hydrophysical characteristics of lake Baikal are presented. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Multiplicity, inclusive, correlation and collective characteristics of multiparticle production processes in K Al, K Au, π Al and π Au interactions at 250 GeV/c are studied with the European Hybrid Spectrometer, providing high statistics and almost 4 π acceptance for final state charged particles. It is shown that the proton energy spectrum practically does not depend on the target atomic weight, but the proton angular distributions reveal a strong A-dependence. In a model independent way, the average number of intranuclear collisions is extracted, and it is shown that their dominant part (60% for Al and 80% for Au) is caused by interactions of the non-leading particles produced in the target fragmentation. The multiplication ratio of the produced particles for the Au nucleus changes from R≃40 at the smallest rapidities in the target fragmentation region, down to R=0.37±0.06 at the largest rapidities in the beam fragmentation region. It is found that the average total longitudinal momentum of the charged products of the beam fragmentation depends weakly on the number of leading hadron (cluster) intranuclear collisions which are characterized by a low inelasticity coefficient 〈 k〉=0.17±0.03. [ABSTRACT FROM AUTHOR]

We report on a study of inclusive π and η meson production in π p and K p interactions at 250 GeV/c beam momentum. The Feynman- x spectrum of π is very similar in shape and normalization to that of negatively charged particles produced in the same experiment. The results are compared with data at other energies and with FRITIOF model predictions. This model overestimates the η cross section by a factor of 2.5. It reproduces the π cross section correctly, but predicts a too hard π x distribution. [ABSTRACT FROM AUTHOR]

The project of an EAS Cherenkov array in the Tunka Valley/Siberia with an area of about 1 km2 is presented. The new array will have a ten times bigger area than the existing TUNKA-25 array and will permit a detailed study of the cosmic ray energy spectrum and the mass composition in the energy range from 1015 to 1018 eV. [ABSTRACT FROM AUTHOR]

New results of 300 hours of operation of the TUNKA array are presented. An improved parametrization of the Cherenkov light lateral distribution function (LDF), based on CORSIKA Monte Carlo simulations and the experiment QUEST, has been used for the reconstruction of EAS parameters. The corrected energy spectrum in the knee region is obtained. The mean depth of the EAS maximum has been derived both from the analysis of LDF steepness and the FWHM of Cherenkov light pulse. The mean mass composition around the knee is estimated. [ABSTRACT FROM AUTHOR]