Extremely high energy cosmic rays

The evidence for the existence of cosmic rays with energies in excess of 10²⁰ eV is now overwhelming. There is so far no indication of the GZK cutoff in the energy spectrum at 5 × 10¹⁹ eV. This conclusion is not firm for lack of statistics. A cutoff would be expected if the sources of the cosmic rays were distributed uniformly throughout the cosmos. The sources of cosmic rays with energy above the GZK cutoff must be at a distance ≤ 100 Mpc, and if they are protons they are very likely to point to these sources. There are no easy explanations how known astrophysical objects can accelerate protons (or atomic nuclei) to these energies. This difficulty has led to speculation that there may be exotic sources such as topological defects which produce these energetic cosmic rays directly along with a copious supply of neutrinos of similar energy. The fluxes of these cosmic rays is very low and large instruments are required to observe them even with modest statistics. One such instrument, the Pierre Auger Observatory, is described. It is designed for all-sky coverage and the construction of its southern site will begin in Argentina in 1999.     

Cosmic ray energy spectrum from measurements of air showers

This review focuses on high-energy cosmic rays in the PeV energy range and above. Of particular interest is the knee of the spectrum around 3 PeV and the transition from cosmic rays of Galactic origin to particles from extra-galactic sources. Our goal is to establish a baseline spectrum from 1014 to 10^20 eV by combining the results of many measurements at different energies. In combination with measurements of the nuclear composition of the primaries, the shape of the energy spectrum places constraints on the number and spectra of sources that may contribute to the observed spectrum.     

Investigation of primary cosmic rays at energies above 10<Superscript>14</Superscript> eV

A search for sources of primary cosmic rays at energies of 10¹⁴–10¹⁵ eV was performed using the special independent KLARA+Khronotron unit at the Tien Shan Mountain Cosmic Ray Station in a joint experiment of the Lebedev Physics Institute (LPI) and the Central Research Institute for Physics (KFKI). A full data bank of standard events, consisting of 30 million extensive air showers (EASes), was analyzed. Analysis results are presented as maps of the directions of EAS arrival in equatorial coordinates in which the standard deviation of the number of events exceeds a certain value. These could be directions from which neutral primary cosmic particles (e.g., gamma ray photons) arrive from sources of primary cosmic rays. A match is found between separate directions with results, obtained on other stations, and the location of pulsars.     

Identifying the spectra of ultrahigh energy cosmic rays from extragalactic sources

The energy spectra of extragalactic sources of cosmic rays are calculated by solving an inverse problem of the transport of cosmic rays with energies of 10¹⁸–10²¹ eV in a Universe filled with background electromagnetic radiation. Calculations are performed using cosmic-ray spectra measured on Earth in Auger experiments. It is assumed that protons and iron nuclei dominate in the composition of a source.     

The search for antimatter in cosmic rays

The search for antimatter in the universe is a page in the history of the Ioffe Physicotechnical Institute (IPTI). Experiments on spacecraft and high-altitude balloons, begun in the 1960s, yielded information on to the presence or absence of antimatter stars or galaxies according to evidence arising in explosive processes in these objects. Antiprotons with energies of 2–5 GeV in galactic cosmic rays were observed at the end of the 1970s in balloon experiments by the Cosmic Spectrometry Laboratory at the IPTI. These studies were done using a magnetic spectrometer at altitudes with a residual pressure of 10 g/cm² with a threshold geomagnetic rigidity of 3 GV. High-latitude experiments in the 1980s, yielding the first measurements of the flux of galactic antiprotons with energies of 0.2–2 GeV, gave some indication of the mechanism by which they are generated. The measured ratios of the fluxes of antiprotons and protons in the cosmic rays are 2.4 _−1.3 ^+2.4 ×10⁻⁴ and 6 ₋₅ ⁺¹⁴ ×10⁻⁵ at energies of 2–5 and 0.2–2 GeV, respectively. Subsequent balloon-borne experiments employing magnetic spectrometers by groups from the USA and Japan have confirmed the results obtained by the IPTI. Experimental and theoretical work on the search for antiparticles in cosmic rays is summarized and the astrophysical consequences of this research are discussed. Experimental data on the detection of antiparticles in galactic cosmic rays indicate that there are no objects made of antimatter within the local group of galaxies. Zh. Tekh. Fiz. 69, 99–103 (September 1999)     

BL Lacertae are probable sources of the observed ultrahigh energy cosmic rays

We calculate an angular correlation function between ultrahigh energy cosmic rays (UHECR), observed by Yakutsk and AGASA experiments, and the most powerful BL Lacertae objects. We find significant correlations with the probability of statistical fluctuation less than 10^?4, including penalty for selecting the subset of the brightest BL Lacs. We conclude that some of the BL Lacs are sources of the observed UHECR and present a list of the most probable candidates.     

Is astronomy possible with neutral ultrahigh energy cosmic ray particles existing in the standard model?

The recently observed correlation between HiRes stereo cosmic ray events with energies E ∼ 10¹⁹ eV and BL Lacertae objects occurs at an angle that strongly suggests that the primary particles are neutral. We analyze whether this correlation, if not a statistical fluctuation, can be explained within the Standard Model, i.e., assuming only known particles and interactions. We have not found a plausible process that can account for these correlations. The mechanism that comes closest—the conversion of protons into neutrons in the IR background of our Galaxy—still underproduces the required flux of neutral particles by about two orders of magnitude. The situation is different at E ∼ 10²⁰ eV, where the flux of cosmic rays at the Earth may contain up to a few percent of neutrons, indicating their extragalactic sources. The text was submitted by the authors in English.     

Promising lines of investigations in the realms of laboratory astrophysics with the aid of powerful lasers

The results of work on choosing and substantiating promising lines of research in the realms of laboratory astrophysics with the aid of powerful lasers are presented. These lines of research are determined by the possibility of simulating, under laboratory conditions, problematic processes of presentday astrophysics, such as (i) the generation and evolution of electromagnetic fields in cosmic space and the role of magnetic fields there at various spatial scales; (ii) the mechanisms of formation and evolution of cosmic gamma-ray bursts and relativistic jets; (iii) plasma instabilities in cosmic space and astrophysical objects, plasma jets, and shock waves; (iv) supernova explosions and mechanisms of the explosion of supernovae featuring a collapsing core; (v) nuclear processes in astrophysical objects; (vi) cosmic rays and mechanisms of their production and acceleration to high energies; and (vii) astrophysical sources of x-ray radiation. It is shown that the use of existing powerful lasers characterized by an intensity in the range of 10¹⁸–10²² W/cm² and a pulse duration of 0.1 to 1 ps and high-energy lasers characterized by an energy in excess of 1 kJ and a pulse duration of 1 to 10 ns makes it possible to perform investigations in laboratory astrophysics along all of the chosen promising lines. The results obtained by experimentally investigating laser plasma with the aid of the laser facility created at Central Research Institute of Machine Building (TsNIIMash) and characterized by a power level of 10 TW demonstrate the potential of such facilities for performing a number of experiments in the realms of laboratory astrophysics.     

Arrival directions and chemical composition of ultrahigh-energy cosmic rays

Chemical composition of ultrahigh-energy cosmic rays is estimated through the reliably determined (both experimentally and theoretically) distribution of the number of showers in the galactic latitude. Experimental data at energies of ～10¹⁹ eV agree with the theoretical calculations, provided that cosmic rays involve predominantly heavy nuclei. An enhanced flux of cosmic rays from the galactic plane is detected at energies of ～10¹⁹ eV.     

Letter: Ultra-High Energy Cosmic Rays and Symmetries of Spacetime

High energy cosmic rays allow probing phenomena that are inaccessible to accelerators. Observation of cosmic rays, presumably protons, with energies beyond 4 × 10¹⁹ eV, the so-called Greisen-Zatsepin-Kuzmin (GZK) cut-off, give origin to two puzzles: How do particles accelerate to such energies ? Are their sources within 50–100 Mpc from Earth, or Lorentz invariance is actually a broken symmetry ? We suggest an astrophysical test to verify the latter alternative and explore a possible connection with an alternative theory of gravity that exhibits preferred-frame effects.     

Cosmic rays and the search for a Lorentz Invariance Violation

This is an introductory review about the ongoing search for a signal of Lorentz Invariance Violation (LIV) in cosmic rays. We first summarise basic aspects of cosmic rays, focusing on rays of ultrahigh energy (UHECRs). We discuss the Greisen-Zatsepin-Kuz’min (GZK) energy cutoff for cosmic protons, which is predicted due to photopion production in the Cosmic Microwave Background (CMB). This is a process of modest energy in the proton rest frame. It can be investigated to a high precision in the laboratory, if Lorentz transformations apply even at factors γ∼O(10¹¹). For heavier nuclei, the energy attenuation is even faster due to photo-disintegration, again if this process is Lorentz invariant. Hence the viability of Lorentz symmetry up to tremendous γ-factors-far beyond accelerator tests-is a central issue.Next, we comment on conceptual aspects of Lorentz Invariance and the possibility of its spontaneous breaking. This could lead to slightly particle dependent “Maximal Attainable Velocities”. We discuss their effect in decays, ?erenkov radiation, the GZK cutoff and neutrino oscillation in cosmic rays.We also review the search for LIV in cosmic γ-rays. For multi-TeV γ-rays, we encounter another possible puzzle related to the transparency of the CMB, similar to the GZK cutoff, due to electron/positron creation and subsequent inverse Compton scattering. The photons emitted in a Gamma Ray Burst occur at lower energies, but their very long path provides access to information not that far from the Planck scale. We discuss conceivable nonlinear photon dispersions based on non-commutative geometry or effective approaches.No LIV has been observed so far. However, even extremely tiny LIV effects could change the predictions for cosmic ray physics drastically.An Appendix is devoted to the recent results by the Pierre Auger Collaboration, in particular the hypothesis that nearby Active Galactic Nuclei-or objects next to them-could be the UHECR sources.     

Capabilities of the Gamma-400 Gamma-ray Telescope for Observation of Electrons and Positrons in the TeV Energy Range

The space-based GAMMA-400 gamma-ray telescope will measure the fluxes of gamma rays in the energy range from ∼20 MeV to several TeV and cosmic-ray electrons and positrons in the energy range from several GeV to several TeV to investigate the origin of gamma-ray sources, sources and propagation of the Galactic cosmic rays and signatures of dark matter. The instrument consists of an anticoincidence system, a converter-tracker (thickness one radiation length, 1 X₀), a time-of-flight system, an imaging calorimeter (2 X₀) with tracker, a top shower scintillator detector, an electromagnetic calorimeter from CsI(Tl) crystals (16 X₀) with four lateral scintillation detectors and a bottom shower scintillator detector. In this paper, the capability of the GAMMA-400 gamma-ray telescope for electron and positron measurements is analyzed. The bulk of cosmic rays are protons, whereas the contribution of the leptonic component to the total flux is ∼10⁻³ at high energy. The special methods for Monte Carlo simulations are proposed to distinguish electrons and positrons from proton background in the GAMMA-400 gamma-ray telescope. The contribution to the proton rejection from each detector system of the instrument is studied separately. The use of the combined information from all detectors allows us to reach a proton rejection of up to ∼1 × 10⁴.

     

Ultra high energy cosmic rays: Identification of possible sources, energy spectra, and propagation

This review is devoted to the problem of the origin of cosmic rays (CR) with energy E >4 × 10¹⁹ eV. The review mainly deals with the hypothesis of CR acceleration in active galactic nuclei (AGN). The review consists of the following five sections: Introduction, three chapters, and Conclusions. The following points are considered in Introduction: shower arrays for detecting ultra high energy cosmic rays (UHECR), the Greisen-Zatsepin-Kuzmin (GZK) cutoff, and the hypotheses of the UHECR origin. Since CRs are of extraterrestrial origin, some astrophysical data used in CR physics are presented in a special section. The identification of UHECR sources with energies E > 4 × 10¹⁹ eV is analyzed in Chapter 2. Chapter 3 deals with CR acceleration in sources and CR escape from sources. Chapter 4 is devoted to particle propagation in intergalactic space with allowance for CR interaction with the microwave background radiation and energy losses (blackbody or GZK cutoff). The propagation of UHECR protons is analyzed and their spectra at the Earth are calculated numerically. In Conclusions, we formulate the results and list the nuclear data needed to develop the model in more detail, namely, to study the propagation of CR nuclei in intergalactic space and to analyze the UHECR composition at the Earth.     

Diffuse extragalactic very-high-energy γ rays

γ Rays with energies E > 4 × 10¹⁹ eV, which are produced upon interactions of cosmic rays with the background radiation in intergalactic space, have been analyzed. The intensity of such γ rays is calculated under different assumptions about the cosmic-ray sources and using different estimates of the nonthermal background radio emission.     

Composition of cosmic rays accelerated in supernova remnants

The kinetic theory of regular acceleration of cosmic rays in supernova remnants is used to investigate the expected chemical composition of the rays. It is shown that the shapes of the calculated profiles of the chemical elements making up the cosmic rays are consistent with experiment wherever the results of measurements are available. The acceleration process is accompanied by relative enrichment of the cosmic rays with heavy elements. If the analogous property of the mechanism underlying the injection of superthermal particles into the acceleration regime is taken into account, such enrichment supports the formation of the required composition of cosmic rays in the energy range up to 10¹⁴–10¹⁵ eV. Zh. éksp. Teor. Fiz. 116, 737–759 (September 1999)     

Testing the correlations between ultrahigh-energy cosmic rays and BL Lac-type objects with HiRes stereoscopic data

Previously suggested correlations of BL Lac-type objects with the arrival directions of the ultrahigh-energy cosmic ray primaries are tested by making use of the HiRes stereoscopic data. The results of the study support the conclusion that BL Lacs may be cosmic ray sources and suggest the presence of a small (a few percent) fraction of neutral primaries at E > 10¹⁹ eV.     

Quasars as sources of ultrahigh-energy cosmic rays

The results are presented that were obtained by analyzing arrival directions for cosmic rays that the Yakutsk array for studying extensive air showers recorded between 1974 and 2002 in the energy region E₀ ≥ 5 × 10¹⁷ eV for zenith angles in the region θ ≤ 60°. It is shown that quasars for which the red shift lies in the region z ≤ 2.5 can be sources of these cosmic rays. Ordered structures are observed in the disposition of quasars and in the cosmic-ray arrival directions. These structures can be associated in one way or another with the large-scale structure of the Universe.     

A method of measurement of extragalactic magnetic fields by TeV gamma ray telescopes

A method is proposed for measuring extragalactic magnetic fields in observations of TeV γ rays from distant sources. Multi-TeV γ rays from these sources interact with the infrared photon background producing secondary electrons and positrons, which can be just slightly deflected by extragalactic magnetic fields before they emit secondary γ rays via inverse Compton scattering of cosmic microwave background photons. Secondary γ rays emitted toward an observer on the Earth can be detected as an extended emission around an initially point source. The energy dependent angular profile of the extended emission is related to the strength of the extragalactic magnetic field along the line of sight. Small magnetic fields B ≤ 10⁻¹² G in the voids of the large scale structure can be measured in this way. The text was submitted by the authors in English     

Efficiency of the production of γ families with halos and the fraction of protons at an energy of 10<Superscript>16</Superscript> eV

γ Families with halos detected in the “Pamir” experiment have been analyzed. Comparison of the experimental data with the results of calculation within the quark-gluon string model (MC0 code) made it possible to determine the efficiency of halo formation by protons, α particles, and heavy nuclei, as well as the fraction of protons in the mass composition of primary cosmic rays at an energy of 10¹⁶ eV. It is shown that halos are formed predominantly by protons. The fraction of protons in the mass composition of primary cosmic rays at an energy of 10¹⁶ eV is 20%.     

Strong signature of the active Sun in 100 years of terrestrial insolation data

Terrestrial solar irradiance data of the Smithsonian Astrophysical Observatory from 1905 to 1954 and of Mauna Loa Observatory from 1958 to 2008 are analyzed. The analysis shows that, with changing solar activity, the atmosphere modifies the solar irradiance on the percentage level, in all likelihood via cosmic ray intensity variations produced by the active sun. The analysis strongly suggests that cosmic rays cause a large part of the atmospheric aerosols. These aerosols show specific absorption and scattering properties due to an inner structure of hydrated ionic centers, most probably of O₂^‐ and O₂⁺ produced by the cosmic rays.