Giant Arrays Research Articles

Measurement of energy spectrum of ultra-high energy cosmic rays

Ultra-high energy cosmic rays (UHECRs) are charged particles of energies above |$10^{18}$| eV that originate outside the Galaxy. Because the flux of the UHECRs at Earth is very small, the only practical way of observing UHECRs is by measuring the extensive air showers produced by UHECRs in the atmosphere. This is done by using air fluorescence detectors and giant arrays of particle detectors on the ground. The Pierre Auger Observatory (Auger) and Telescope Array (TA) are two large cosmic ray experiments that use such techniques and cover 3000 and 700 km|$^2$| areas on the ground, respectively. In this paper, we present the UHECR spectrum reported by TA, using an exposure of 6300 km|$^2$| sr yr accumulated over 7 years of data taking, and the corresponding result of Auger, using 10 years of data with a total exposure exceeding 50 000 km|$^2$| sr yr. We review the astrophysical interpretation of the two measurements, and discuss their systematic uncertainties.

Giant Vesicle Arrays: A Simple and Versatile Method for the Formation of Arrays of Giant Vesicles with Controlled Size and Composition (Adv. Mater. 47/2013)

Giant Vesicle Arrays: A Simple and Versatile Method for the Formation of Arrays of Giant Vesicles with Controlled Size and Composition (Adv. Mater. 47/2013)

COMPARING THE ENERGY SPECTRA OF ULTRAHIGH ENERGY COSMIC RAYS MEASURED WITH EXTENSIVE AIR SHOWER ARRAYS

The energy spectra of ultra-high energy cosmic rays (CRs) measured with giant extensive air shower (EAS) arrays exhibit discrepancies between the flux intensities and/or estimated CR energies exceeding experimental errors. The well-known intensity correction factor due to the dispersion of the measured quantity in the presence of a rapidly falling energy spectrum is insufficient to explain the divergence. Another source of systematic energy determination error is proposed concerning the charged particle density measured with the surface arrays, which arises due to simplifications (namely, the superposition approximation) in nucleus-nucleus interaction description applied to the shower modeling. Making use of the essential correction factors results in congruous CR energy spectra within experimental errors. Residual differences in the energy scales of giant arrays can be attributed to the actual overall accuracy of the EAS detection technique used. CR acceleration and propagation model simulations using the dip and ankle scenarios of the transition from galactic to extragalactic CR components are in agreement with the combined energy spectrum observed with EAS arrays.

On the estimate of the energy of the nuclei of primary cosmic radiation generating extensive air showers

The analysis of the systematic errors in the determination of the energy of the particles of primary cosmic radiation that are inherent in the method for measuring extensive air showers (EASs) indicates the necessity of the exact inclusion of fragmentation in the nuclear interactions. The application of such a model developed for describing the experiments at the Relativistic Heavy Ion Collider improves the agreement between the energy spectra of the ultrahigh-energy cosmic rays measured at giant EAS arrays. It has been shown that the difference between the measured primary cosmic radiation flux intensities and the energies of the primary particles is within the methodical and instrumental errors. The real accuracy of the EAS method of studying ultrahigh-energy cosmic rays has been estimated using the data from six arrays.

A search for extragalactic sources of cosmic rays in the ultra-high energy domain

The arrival directions of ultra-high energy cosmic rays detected with the Yakutsk extensive air shower array are analyzed in comparison with the available data from other giant arrays. A correlation with the coordinates of active galaxy nuclei as hypothesized sources of ultra-high energy cosmic rays is sought for.

Exploring arrival directions of UHECRs with the Yakutsk array

The data on arrival directions of ultra-high energy cosmic rays (UHECRs) detected with the Yakutsk array are analyzed. The work is induced by the recent claim of the Pierre Auger collaboration for the significant correlation found between UHECRs and positions of nearby Active Galactic Nuclei (AGN) on the celestial sphere; and no correlation the HiRes collaboration stands for. Conflicting data of four giant arrays concern possible extragalactic sources of UHECRs and appeal to the profound analysis and to the future data from the Telescope Array/Northern Auger Observatory.

Characteristics and Performance of the GAW Experiment for a Large Field of View Cerenkov Gamma-ray Telescope

One of the intents of the ground-based gamma-ray astronomy is to obtain a sky survey in the TeV energy region, and nowadays this target can be reached with giant arrays of telescopes, which however need many pointings due to their small field of view. A different approach is on the basis of GAW, acronym for Gamma Air Watch, an array of three relatively small Cerenkov telescopes which differentiate from the existing and presently planned telescopes for two main features: the adoption of a refractive optics system as light collector with a large field of view capability, and the use of single photoelectron counting as detector working mode. During a first phase, the focal plane detector of the GAW telescopes will be implemented in a reduced configuration to test the sensitivity and to prove the feasibility of the method; then the focal plane will be enlarged to cover a field of view of 24°×24°; pointing along different North-South directions, GAW would reach a survey of 360°×60° region of the sky. In this paper, the GAW expected performance are reported as evaluated in the case of the Calar Alto site, Spain, 2150 m a.s.l., where GAW is planned to be located within 2007. GAW is a collaboration effort of Research Institutes in Italy, Portugal and Spain.

The continuity of the primary cosmic ray spectra measured by classical and giant EAS arrays

The extrapolation of the original cosmic ray primary spectrum derived from the size spectrum measured in the Akeno classical EAS array coincides with the spectrum measured recently by the HiRes Stereo experiment. After revisiting the calibrations carried in the overlapping energy region around 1018 eV, we discuss the consequences of the different approaches in classical arrays and giant surface arrays. The data are obtained from the size spectrum registration in the Akeno experiment with a modest space grid of 30–100 m, instead of 1 km or more in giant arrays using density estimators in place of size and different absorption treatments for inclined cascades. While the analysis of those circumstances suggests a reduction of the energy converted from the estimators in giant surface arrays, the consistency of classical and fluorescence measurements gives more support to the GZK prediction.

Ultrahigh-energy cosmic rays: Possible origin and spectrum

The complicated shape of the cosmic ray spectrum recorded by giant arrays in the energy range 1017–1020 eV is analyzed. It is shown that in the energy region ∼1018–1019 eV the spectrum probably coincides with the injection spectrum whose exponent is equal approximately to 3.2–3.3. The flatter component in the energy region (3.2–5.0)×1019 eV is due to braking of extragalactic protons on primordial photons (the cosmic background radiation). At energies exceeding 3.2×1019 eV the spectrum does not have a blackbody cutoff. The possibility of determining the distances at which cosmic rays originate and investigating the evolution of their sources on the basis of ultrahigh-energy cosmic ray data is discussed.

Possible origin and spectrum of ultrahigh-energy cosmic rays

The complicated form of the cosmic-ray spectrum recorded in the energy range 1017–1020 eV by giant detector arrays is analyzed. It is shown that the spectrum in the region 1018–1019 eV is apparently identical to the injection spectrum with power-law exponent approximately equal to 3.2–3.3. The flat component in the region (3.2–5)×1019 eV is due to the braking of extragalactic protons by relict photons. The spectrum apparently has no blackbody cutoff at energies above 3.2×1019 eV.

Notes on ultra-high-energy interaction processes

An attempt is made to develop a picture of ultra-high-energy interaction processes which is consistent with the known data of cosmic rays. At low energies these data are drawn from the results of emulsions, emulsion chambers and other installations (such as the Echo Lake facility). At high energies these data are inferred from the response of the giant arrays designed to measure air showers initiated by primaries with incident energy (E0) as high as (1010÷1020) eV. A possible link between multiplicity increase and observed transverse momenta is discussed in terms of four-momentum damping. In addition, resonance formation and expected average elasticity are considered.