The ground-based large-area wide-angle γ-ray and cosmic-ray experiment HiSCORE

The question of the origin of cosmic rays and other questions of astroparticle and particle physics can be addressed with indirect air-shower observations above 10 TeV primary energy. We propose to explore the cosmic ray and γ-ray sky (accelerator sky) in the energy range from 10 TeV to 1 EeV with the new ground-based large-area wide angle (ΔΩ ∼ 0.85 sterad) air-shower detector HiSCORE (Hundred^∗i Square-km Cosmic ORigin Explorer). The HiSCORE detector is based on non-imaging air-shower Cherenkov light-front sampling using an array of light-collecting stations. A full detector simulation and basic reconstruction algorithms have been used to assess the performance of HiSCORE. First prototype studies for different hardware components of the detector array have been carried out. The resulting sensitivity of HiSCORE to γ-rays will be comparable to CTA at 50 TeV and will extend the sensitive energy range for γ-rays up to the PeV regime. HiSCORE will also be sensitive to charged cosmic rays between 100 TeV and 1 EeV.     

Cosmic ray detection on the Foton-M2 satellite by a track etch detector stack

In the frame of the European Space Agency (ESA) project called “Biology and Physics in Space”, the returning satellite, Foton-M2, carried an open-to-space exposure platform outside of the satellite body, called as BIOPAN-5, loaded with exo-biological experiments and facilities for radiation dosimetry (RADO). One of the RADO experiments was dedicated to the detection of the primary galactic cosmic rays (GCR) and secondary neutrons by a track etch detector stack. The daily absorbed dose (D) and dose equivalent (H) were calculated from the experimental LET spectra (LET > 10 keV/μm). Under a shielding of ∼2.8 g/cm² the averaged H was found to be 658 ± 8 μSv/d, with a quality factor (Q) of 6.2 ± 1.2. The LET spectra showed a local peak at ∼105 keV/μm suggesting that the majority of tracks were created by trapped protons as it has been predicted by calculations. The low LET dose of the cosmic radiation was determined by 4 TLD stacks, and the total dose was found to be 795 ± 14 μSv/d.     

Enhancing the ATIC charge resolution

The Advanced Thin Ionization Calorimeter (ATIC) experiment is designed to investigate the charge composition and energy spectra of primary cosmic rays over the energy range from about 10¹¹ to 10¹⁴ eV during Long Duration Balloon (LDB) flights from McMurdo, Antarctica. Currently, analysis from the ATIC-1 test flight and ATIC-2 science flight is underway and preparation for a second science flight is in progress. Charge identification of the incident cosmic ray is accomplished, primarily, by a pixilated Silicon Matrix detector located at the very top of the instrument. While it has been shown that the Silicon Matrix detector provides good charge identification even in the presence of electromagnetic shower backscatter from the calorimeter, the detector only measures the charge once. In this paper, we examine use of the top scintillator hodoscope detector to provide a second measure of the cosmic ray charge and, thus, improve the ATIC charge identification.     

First measurements of cosmic-ray nuclei at high energy with CREAM

The balloon-borne cosmic-ray experiment CREAM-I (Cosmic-Ray Energetics And Mass) recently completed a successful 42-day flight during the 2004–2005 NASA/NSF/NSBF Antarctic expedition. CREAM-I combines an imaging calorimeter with charge detectors and a precision transition radiation detector (TRD). The TRD component of CREAM-I is targeted at measuring the energy of cosmic-ray particles with charges greater than Z ∼ 3. A central science goal of this effort is the determination of the ratio of secondary to primary nuclei at high energy. This measurement is crucial for the reconstruction of the propagation history of cosmic rays, and consequently for the determination of their source spectra. First scientific results from this instrument are presented.     

Study of the 27-day variations of the galactic cosmic ray intensity and anisotropy

We demonstrate that the general features of the radial and azimuthal components of the anisotropy of galactic cosmic rays can be studied by the harmonic analysis method using data from an individual neutron monitor with cut off rigidity <5 GV. In particular, we study the characteristics of the 27-day (solar rotation period) variations of the galactic cosmic ray intensity and anisotropy, solar wind velocity, interplanetary magnetic field strength and sunspot number. The amplitudes of the 27-day variations of the galactic cosmic ray anisotropy are greater, and the phases more clearly established, in A > 0 polarity periods than in A < 0 polarity periods at times of minimum solar activity. The phases of the 27-day variations of the galactic cosmic rays intensity and anisotropy are opposite with respect to the similar changes of the solar wind velocity in A > 0 polarity periods. No significant dependence of the amplitude of the 27-day variation of the galactic cosmic ray anisotropy on the tilt angle of the heliospheric neutral sheet is found. Daily epicyclegrams obtained by Chree’s method show that the 27-day variations of the galactic cosmic ray anisotropy during A > 0 polarity periods follow elliptical paths with the major axes oriented approximately along the interplanetary magnetic field. The paths are more irregular during A < 0 polarity periods.     

On the origin of ultrahigh energy cosmic rays

The origin of cosmic rays with energy E ? 10¹⁸ eV is a long-standing problem in astrophysics. The development of ever larger detectors has brought in key experimental results in the past decade, most particularly the detection of a cut-off at the expected position for the long sought Greisen–Zatsepin–Kuzmin suppression as well as evidence for large scale anisotropies. This paper summarizes and discusses the recent achievements in this field.     

Propagation of secondary antiprotons and cosmic rays in the Galaxy

Recent measurements of the cosmic ray (CR) antiproton flux have been shown to challenge existing CR propagation models. It was shown that the reacceleration models designed to match secondary to primary nuclei ratios (e.g., B/C) produce too few antiprotons. In the present paper, we discuss one possibility to overcome these difficulties. Using the measured antiproton flux and B/C ratio to fix the diffusion coefficient, we show that the spectra of primary nuclei as measured in the heliosphere may contain a fresh local “unprocessed” component at low energies perhaps associated with the Local Bubble, thus decreasing the measured secondary to primary nuclei ratio. The independent evidence for SN activity in the solar vicinity in the last few Myr supports this idea. The model reproduces antiprotons, B/C ratio, and elemental abundances up to Ni (Z ⩽ 28). Calculated isotopic distributions of Be and B are in perfect agreement with CR data. The abundances of three “radioactive clock” isotopes in CR, ¹⁰Be, ²⁶Al, ³⁶Cl, are all consistent and indicate a halo size z_h ∼ 4 kpc based on the most accurate data taken by the ACE spacecraft.     

Empirical model of cosmic ray spectrum in energy interval 1 MeV–100 GeV during 11-year solar cycle

The galactic cosmic rays (GCR) are the main ionization source at altitude of ∼3–35 km in the atmosphere. For high latitude anomalous cosmic ray (ACR) component has also a significant influence on the atmospheric ionization. We propose an empirical model for differential spectra D(E) of galactic and anomalous cosmic rays in energy interval 1 MeV–100 GeV during solar cycle. In the model data are used which cover three solar cycles: 20, 22 and 23. The LEAP87, IMAX92, CAPRICE94, AMS98 and BESS experimental spectra for protons and alpha particles are fitted to the proposed empirical model. The modulated GCR differential spectra are compared with force-field approximation to the one-dimensional transport equation and with solutions of two-dimensional cosmic ray transport equation. For experimental spectra, the calculation of the model parameters is performed by Levenberg–Marquardt algorithm, applied to the special case of least squares. Algorithm that combines the rapid local convergence of Newton–Raphson method with globally convergent method for non-linear systems of equations is applied for theoretically obtained differential spectra. The described programmes are realized in algorithmic language C++. The proposed model gives practical possibility for investigation of experimental data from measurements of galactic cosmic rays and their anomalous component.     

Modeling and data analysis of a Forbush decrease

We study the Forbush decrease of the galactic cosmic ray intensity observed in 9–25 September 2005 using the experimental data and a newly developed time-dependent three dimensional modeling. We analyze neutron monitors and muon telescopes, and the interplanetary magnetic field data. We demonstrate a clear relationship between the rigidity (R) spectrum exponent (γ) of the Forbush decrease and the exponent (ν) of the power spectral density of the components of the interplanetary magnetic field in the frequency range of ∼ 10⁻⁶–10 ⁻⁵ Hz. We confirm that an inclusion of the time-dependent changes of the exponent ν makes the newly developed nonstationary three dimensional model of the Forbush decrease compatible with the experimental data. Also, we show that the changes of the rigidity spectrum exponent γ does not depend on the level of convection of the galactic cosmic rays stream by solar wind; depending on the changes of the exponent ν, i.e. on the state of the turbulence of the interplanetary magnetic field.     

Depth dependency of neutron density produced by cosmic rays in the lunar subsurface

Depth dependency of neutrons produced by cosmic rays (CRs) in the lunar subsurface was estimated using the three-dimensional Monte Carlo particle and heavy ion transport simulation code, PHITS, incorporating the latest high energy nuclear data, JENDL/HE-2007. The PHITS simulations of equilibrium neutron density profiles in the lunar subsurface were compared with the measurement by Apollo 17 Lunar Neutron Probe Experiment (LNPE). Our calculations reproduced the LNPE data except for the 350–400 mg/cm² region under the improved condition using the CR spectra model based on the latest observations, well-tested nuclear interaction models with systematic cross section data, and JENDL/HE-2007.     

The Tien-Shan mountain cosmic ray station of the Ionosphere Institute of Kazakhstan Republic

The mountain cosmic ray (CR) station of the Ionosphere Institute of Kazakhstan Republic (CR station Alma-Ata B, 43.1N latitude, 76.6E longitude, geomagnetic rigidity cutoff 6.69 GV) is a center for an experimental study of the non-stationary processes caused by cosmic rays of different origin in the interplanetary and near-Earth space, so as their influence on the state of the Earth’s magnetosphere and the upper atmosphere layers. This paper summarizes efforts performed over the years by the Almaty CR group till its present status.     

Fluxes and nuclear abundances of cosmic rays inside the magnetosphere using a transmission function approach

At 1 AU and outside the Earth’s magnetosphere, the relative abundances to protons for He (He/p), C (C/p) and Fe (Fe/p) nuclei were calculated using the observation data of AMS-01 (for p and He) and HEAO-3 (for C and Fe) above 0.8 GeV/nucleon. In addition, the transmission function (TF) for the GCR propagation inside the magnetosphere was evaluated using the IGRF and T96 (introduced by Tsyganenko and Stern) models to obtain permitted and forbidden trajectories inside the magnetosphere. The TF allowed one to derive the primary He-nuclei fluxes in the same geomagnetic regions of AMS-01 observations. These fluxes were found in good agreement with the observation data. Furthermore inside the magnetosphere in addition to the flux of helium, it allowed one to obtain those of the primary p, C, and Fe nuclei and the relative abundances of He, C and Fe nuclei to protons from the same observation data of AMS-01 and HEAO-3 above ≈0.8 GeV/nucleon. Up to a geomagnetic latitude of ≈45.84°, the relative isotopic abundances were found to depend on the mass number I_isot and, on average, range from a factor ≈2.31 up to ≈3.35 larger than those outside the magnetosphere at 1 AU. Thus, the magnetospheric isotopic/nuclear relative abundances differ from those inside the solar cavity and those in the interstellar space. The usage of the TF approach can allow one to determine the nuclear abundances in the magnetosphere at any geomagnetic latitude and, thus, any orbit, provided that the CR spectra are determined at 1 AU.     

Search for antihelium: Progress with BESS

In this paper, we report searches for antihelium in cosmic rays using two recently flown magnetic rigidity spectrometers. BESS-TeV had extended rigidity with an MDR of 1.4 TV and had a flight duration of one day. BESS-Polar was optimized for collecting power. It was flown for 8.5 days and had an MDR of 240 GV. The former flight allows us to explore a previously unexplored rigidity band and the latter flight yields a factor of three improvement in the overall BESS limit. No antihelium candidate was found in the rigidity ranges of 1–500 GV, and 0.6–20 GV, among 7 × 10⁴ events taken with BESS-TeV, and 8 × 10⁶ events taken with BESS-Polar, respectively.     

The IGY and beyond: A brief history of ground-based cosmic-ray detectors

The state of art of ground-based cosmic-ray research from its discovery to present is reviewed. After discovery of cosmic rays by Hess in 1912, the nature of the primary and secondary radiation was established from recordings by a variety of instruments, sensitive to various components of cosmic rays and operated at different latitudes, longitudes and altitudes, including instruments carried by balloons. The IGY formalized international co-operation and coordinated study of cosmic rays, which is vital for meaningful interpretation of cosmic-ray data. Data collected at different geographic locations require an effective cutoff rigidity as a data ordering parameter. This parameter is obtained from tracing trajectories of primary cosmic rays in the Earth’s magnetic field. After 50 years the world’s neutron monitor network remains still the backbone for studying intensity variations of primary cosmic rays in the rigidity ranges between 1 and 15 GV, associated with transport and with transient events. Also the penetrating muon and neutrino components of secondary cosmic rays have a long history of recording and fundamental problem investigations. Valuable data about composition and spectrum of primary cosmic rays in ever increasing high-energy regions have been obtained during the years of investigations with various configurations and types of extensive air shower detectors. The culture of personal involvement of the physicist in carrying out experiments and data acquisition characterized the continued vitality of cosmic-ray investigations ranging from its atmospheric, geomagnetic and heliospheric transport through to its solar and astrophysical origins.     

The scaler mode in the Pierre Auger Observatory to study heliospheric modulation of cosmic rays

The impact of the solar activity on the heliosphere has a strong influence on the modulation of the flux of low energy galactic cosmic rays arriving at Earth. Different instruments, such as neutron monitors or muon detectors, have been recording the variability of the cosmic ray flux at ground level for several decades. Although the Pierre Auger Observatory was designed to observe cosmic rays at the highest energies, it also records the count rates of low energy secondary particles (the scaler mode) for the self-calibration of its surface detector array. From observations using the scaler mode at the Pierre Auger Observatory, modulation of galactic cosmic rays due to solar transient activity has been observed (e.g., Forbush decreases). Due to the high total count rate coming from the combined area of its detectors, the Pierre Auger Observatory (its detectors have a total area greater than 16,000 m²) detects a flux of secondary particles of the order of ∼10⁸ counts per minute. Time variations of the cosmic ray flux related to the activity of the heliosphere can be determined with high accuracy. In this paper we briefly describe the scaler mode and analyze a Forbush decrease together with the interplanetary coronal mass ejection that originated it. The Auger scaler data are now publicly available.     

Evolution of Dst index,cosmic rays and global temperature during solar cycles 20–23

We have studied conditions in interplanetary space, which can have an influence on galactic cosmic ray (CR) and climate change. In this connection the solar wind and interplanetary magnetic field parameters and cosmic ray variations have been compared with geomagnetic activity represented by the equatorial Dst index from the beginning 1965 to the end of 2012. Dst index is commonly used as the solar wind–magnetosphere–ionosphere interaction characteristic. The important drivers in interplanetary medium which have effect on cosmic rays as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Because of this CMEs, coronal holes and the solar spot numbers (SSN) do not adequately reflect peculiarities concerned with the solar wind arrival to 1 AU. Therefore, the geomagnetic indices have some inestimable advantage as continuous series other the irregular solar wind measurements. We have compared the yearly average variations of Dst index and the solar wind parameters with cosmic ray data from Moscow, Climax, and Haleakala neutron monitors during the solar cycles 20–23. The descending phases of these solar cycles (CSs) had the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst variations. They also had effects on cosmic rays variations. We show that long-term Dst variations in these solar cycles were correlated with the cosmic ray count rate and can be used for study of CR variations. Global temperature variations in connection with evolution of Dst index and CR variations is discussed.     

How cosmic rays were discovered and why they received this misnomer

As many great discoveries, the phenomenon of cosmic rays was discovered mainly accidentally, during investigations that sought to answer another question: what are sources of air ionization? This problem became interesting for science about 230 years ago in the end of the 18th century, when physics met with a problem of leakage of electrical charge from very good isolated bodies. We describe the history how step by step cosmic rays was discovered and why this phenomenon received misnomer, how in cosmic rays was discovered the first antiparticle – positron. These discoveries were recognized among greatest in the 20th Century and were awarded by Nobel Prize.     

Detection of the high energy component of Jovian electrons in Low Earth Orbit with the PAMELA experiment

The PAMELA experiment is devoted to the study of cosmic rays in Low Earth Orbit with an apparatus optimized to perform a precise determination of the galactic antimatter component of c.r. It is constituted by a number of detectors built around a permanent magnet spectrometer. PAMELA was launched in space on June 15th 2006 on board the Russian Resurs-DK1 satellite for a mission duration of 3 years. The characteristics of the detectors, the long lifetime and the orbit of the satellite, will allow to address several aspects of cosmic-ray physics. In this work we discuss the observational capabilities of PAMELA to detect the electron component above 50 MeV. The magnetic spectrometer allows a detailed measurement of the energy spectrum of electrons of galactic and Jovian origin. Long term measurements and correlations with Earth–Jupiter 13 months synodic period will allow to separate these two contributions and to measure the primary electron Jovian component, dominant in the 50–70 MeV energy range. With this technique it will also be possible to study the contribution to the electron spectrum of Jovian e⁻ reaccelerated up to 2 GeV at the Solar Wind Termination Shock.     

Cosmic ray acceleration by supernova shocks

We analyse the results of recent measurements of nonthermal emission from individual supernova remnants (SNRs) and their correspondence to the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is shown that the theory fits these data in a satisfactory way and provides the strong evidences for the efficient CR production in SNRs accompanied by significant magnetic field amplification. Magnetic field amplification leads to considerable increase of CR maximum energy so that the spectrum of CRs accelerated in SNRs is consistent with the requirements for the formation of Galactic CR spectrum up to the energy ∼10¹⁷ eV.