R.A. Antonov

The new Tien-Shan Atmospheric Čerenkov Telescope (TACT). Contemporary status: all-particle spectrum measured

Abstract Results for the primary cosmic ray energy spectrum at 100–1000 TeV, data on the lateral distribution function for Cerenkov light of EAS and curvature of Cerenkov photon front are presented. Measurements were carried out using an array for observation of discrete gamma-sources in the TeV region.

Method for measuring the PCR proton spectrum in the energy range of > 1016 eV

Criteria for selecting proton events among the total sequence of events from primary nuclei of cosmic rays with zenith angles θ < 20° are analyzed in the energy region of E0 ≈ 1016 eV. These criteria are concretized for the case of the SPHERE-2 experiment geometry. The QGSJET-I and QGSJET-II model calculations show that the criteria based on the shape of the transverse distribution of Cherenkov light allow detection of more than 10% of proton events and rejection of 99% nuclear events.

Primary cosmic ray spectrum measured using Cherenkov light reflected from the snow surface

The experimental data obtained using Cherenkov light of EAS, reflected from the snow surface of the Big Alma—Ata Lake (Kazakhstan) are presented. This method makes it possible to have a large area using a simple compact detector. About 9000 events were detected within 55 hours. The balloon—borne measurements in the energy range 1–10000 PeV are planned.

Event-by-event study of CR composition with the SPHERE experiment using the 2013 data

We present an event-by-event study of cosmic ray (CR) composition with the reflected Cherenkov light method. The fraction of CR light component above 5 PeV was reconstructed using the 2013 run data of the SPHERE experiment which observed optical Vavilov-Cherenkov radiation of extensive air showers, reflected from snow surface of Lake Baikal. Additionally, we discuss a possibility to improve the elemental groups separability by means of multidimensional criteria.

Cosmic ray study by means of reflected EAS Cherenkov light method with the SPHERE-2 detector

The approach to cosmic ray (CR) study with reflected optical Vavilov-Cherenkov radiation (Cherenkov light) was proposed long ago. At present the SPHERE-2 detector is the only existing apparatus that have detected a significant sample of extensive air showers (EAS) by means of this method. At the same time the recorded data allows detailed reconstruction of EAS lateral distribution function (LDF) used to study primary CR mass composition. We report on the status and results of the SPHERE experiment with the emphasis on the peculiarities of the reflected Cherenkov light technique. Detector response simulation was performed by means of full direct Monte Carlo simulation with account of realistic background and noise patterns recorded during the observational runs. Instrumental acceptance was simulated for various energies, charge numbers and zenith angles of primary nuclei. Primary energy of observed showers was estimated with a typical statistical uncertainty 10-20% depending on the primary nucleus parameters. The typical systematic uncertainty of the estimated energy vs the primary charge number was found to be below 3%. The primary all-nuclei spectrum was reconstructed. The fraction of light nuclei vs energy in the energy range 10-100 PeV was estimated by means of an event-by-event approach using the LDF steepness parameter.

Detector for the ultrahigh energy cosmic rays composition study in Antarctica

The main purpose of the Sphere–Antarctica project is connected to the fundamental problems of the cosmic ray physics and general astrophysics - the determination of the energy and mass composition of cosmic ray particles of ultra high and extremely high energies 1018 − 1020 eV. In the energy region above 6 1019 eV modern experiments (Telescope Array and Pierre Auger Observatory) observed anisotropy and the clustering of arrival directions of cosmic rays in some areas. The scientific importance of this problem stems from the lack of generally accepted acceleration mechanism of the CR particles above 3 1018 eV, the unknown nature of the sources of such particles, the inconsistencies of the results of major experiments in the part of the mass of CR composition and the discrepancy of experimental and model data. Scientific novelty of this project is in the methodology registration of the extensive air showers over a large area ~ 600 km2 from an altitude 30 km, that allows to measure the two optical components of the shower Vavilov–Cherenkov radiation and fluorescence light by the same SiPM sensitive elements of the detector simultaneously.

The prototype SPHERE-Antarctica station and the possibility of using silicon PMTs to detect the Cherenkov and fluorescent light of EASes

The design for a balloon instrument to study the energy spectrum and mass composition of primary cosmic rays at energies exceeding 1018 eV is presented. It is planned to conduct the experiment during Antarctica’s polar night. The equipment allows the separate registration of fluorescent light (FL) and Cherenkov radiation (CR) in each event. The advantages of the experiment over existing ground-based installations and future orbiting stations are discussed. A way of separating FL from CR with light filters and optical silicon detectors is described.

Detection of reflected Cherenkov light from extensive air showers in the SPHERE experiment as a method of studying superhigh energy cosmic rays

Although a large number of experiments were carried out during the last few decades, the uncertainty in the spectrum of all nuclei of primary cosmic rays (PCRs) with superhigh energies is still high, and the results of many experiments on nuclear composition of PCRs are contradictory. An overview of the SPHERE experiment on detecting Vavilov-Cherenkov radiation from extensive air shower (EAS) reflected from a ground snow surface is given. A number of experimental studies implementing this method are presented and their results are analyzed. Some other popular methods of studying PCRs with superhigh energies (E 0 > 1015 eV) and their main advantages and drawbacks are briefly considered. The detecting equipment of the SPHERE-2 experiment and the technique of its calibration are considered. The optical properties of snow, which are important for experiments on reflected Cherenkov light (CL) from EAS, are discussed and the history of observing reflected EAS CL is described. The algorithm of simulating the detector response and calculating the fiducial acceptance of shower detection is described. The procedure of processing the experimental data with a subsequent reconstruction of the spectrum of all PCR nuclei and analysis of the mass composition is shown. The first results of reconstructing the spectrum and separating groups of cosmic-ray nuclei with high energies in the SPHERE-2 experiment are presented. Main sources of systematic errors are considered. The prospects of developing the technique of observation of reflected EAS CL in future experiments are discussed.

Investigation of SPHERE-2 data sensitivity to chemical composition of primary cosmic rays

A new method for assessing the type of particles of primary cosmic rays in the energy range of 10–1000 PeV for individual events recorded by the SPHERE-2 facility is presented. The method is based on comparing images of recorded events and simulated events, while assuming various types of primary particles with allowance for measuring errors. The aim of the study is to find the limits of sensitivity in determining of the chemical composition of ultrahigh-energy primary cosmic rays using the detection of reflected Cherenkov light generated by extensive air showers (EASes).

Status of the SPHERE experiment

Here is presented the current state of the SPHERE-2 balloon-borne experiment. The detector is elevated up to 1 km above the snow surface and registers the reflected Vavilov-Cherenkov radiation from extensive air showers. This method has good sensitivity to the mass-composition of the primary cosmic rays due to its high resolution near the shower axis. The detector consists of a 1500 mm spherical mirror with a 109 PMT cluster in its focus. The electronics record a signal pulse profile in each PMT. In the last 2 years the detector was upgraded: time resolution of pulse registration was enhanced up to 12.5 ns, channel sensitivity was increased by a factor of 3, a new LED-based relative PMT calibration method was introduced, and new hardware and etc. was installed.