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Tunka-HiSCORE (HiSCORE: Hundred Square-km Cosmic Origin Explorer) is a new Cherenkov EAS arrayfor multi-TeV γ ray astronomy and cosmic ray studies. The array will consist of wide-angle (0.6 sr)optical stations with 150 m distance between individual stations. The array will be constructed in severalstages: beginning with a 1 km 2 array at the first stage up to 100 km at the last stage. The first threestations have been installed during 2012 in Tunka Valley (50 km from the Southern tip of Lake Baikal) atthe site of the Tunka-133 array. We describe the construction of the optical stations and the array DAQ,and present the first results of common operation of the new optical stations with the Tunka-133 array.& 2013 Elsevier B.V. All rights reserved. 1. IntroductionWe propose to explore the so far poorly measured cosmic ray andγ ray sky in the energy region from 20 TeV to 100 PeV with thelarge area wide-angle cosmic ray and γ ray detector Tunka-HiSCORE[1,2]. Tunka-HiSCORE will be a non-imaging Cherenkov light-frontsampling array with large sensitive area (0.5 m

We present physical motivations and advantages of the new gamma-observatory TAIGA (Tunka Advanced Instrument for cosmic ray physics and gamma-ray astronomy). TAIGA will be located in the Tunka valley, 50 km to the west of Lake Baikal, at the same place as the integrating air Cherenkov detector for cosmic rays Tunka-133. The TAIGA array is a complex, hybrid detector for ground-based gamma-ray astronomy for energies from a few TeV to several PeV as well as for cosmic ray studies from 100 TeV to several EeV. The array will consist of a wide angle Cherenkov array – TAIGA-HiSCORE with 5km2 area, a net of 16 IACT telescopes (with FOV of about 9.72°×9.72°) as well as muon and other detectors. We present the current status of the array construction.

Up to several 10s of TeV, Imaging Air Cherenkov Telescopes (IACTs) have proven to be the instruments of choice for GeV/TeV gamma-ray astronomy due to their good reconstrucion quality and gamma-hadron separation power. However, sensitive observations at and above 100 TeV require very large effective areas (10 km2 and more), which is difficult and expensive to achieve.The alternative to IACTs are shower front sampling arrays (non-imaging technique or timing-arrays) with a large area and a wide field of view. Such experiments provide good core position, energy and angular resolution, but only poor gamma-hadron separation. Combining both experimental approaches, using the strengths of both techniques, could optimize the sensitivity to the highest energies.The TAIGA project plans to combine the non-imaging HiSCORE [8] array with small (~10m2) imaging telescopes. This paper covers simulation results of this hybrid approach.

The gamma-ray energy regime beyond 10 TeV is crucial for the search for the most energetic Galactic accelerators. The energy spectra of most known gamma-ray emitters only reach up to few 10s of TeV, with 80 TeV from the Crab Nebula being the highest energy so far observed significantly. Uncovering their spectral shape up to few 100 TeV could answer the question whether some of these objects are cosmic ray Pevatrons, i.e. Galactic PeV accelerators.Sensitive observations in this energy range and beyond require very large effective detector areas of several 10s to 100 square-km. While imaging air Cherenkov telescopes have proven to be the instruments of choice in the GeV to TeV energy range, very large area telescope arrays are limited by the number of required readout channels per instrumented square-km (due to the large number of channels per telescope). Alternatively, the shower-front sampling technique allows to instrument large effective areas and also naturally provides large viewing angles of the instrument. Solely measuring the shower front light density and timing (hence timing- arrays), the primary particle properties are reconstructed on the basis of the measured lateral density function and the shower front arrival times. This presentation gives an overview of the technique, its goals, and future perspective.

The calculations of source spectra of extragalactic cosmic rays with ultra high energies are made based on the solution of inverse problem for a system of transport equations that describes the propagation of protons and nuclei with energies 1018 to 1021 eV in the expanding Universe filled with the background radiation. It is assumed that protons and Iron nuclei are the most abundant species in the sources. The data from the Auger experiment is used to illustrate the method.