• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.413-420
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• 2004

The current state and future prospects of ultra high energy cosmic ray physics are reviewed. These cosmic rays with energies well above $10^{18}$ eV are messengers of an unknown extremely high-energy universe.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.57.2-57.2
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• 2010

Cosmic rays with energy exceeding 10^18eV are referred to as Ultra high energy cosmic rays (UHECRs). UHECR experiments have utilized air shower simulations to estimate the properties of cosmic rays. Telescope array (TA) experiment has used COSMOS and CORSIKA mainly; the Monte Carlo codes of CORSIKA and COSMOS simulate the evolution of extensive air showers in the atmosphere initiated by photons, hadrons or nuclei UHECRs. We compare the simulations from CORSIKA and COSMOS. Comparison has shown noticeable differences at the ground distributions, longitudinal distributions, Calorimetric energy, and Xmax value. The implications of our results are discussed.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.70.2-70.2
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• 2011

Ultra-high energy cosmic rays(UHECRs) refer cosmic rays with energy above 1018eV. UHECR experiments have employed air shower simulations to quantify the properties of cosmic rays. Using COSMOS and CORSIKA, we have produced a library of over 15000 thinned extensive air shower(EAS) simulations with the primary energies ranging from 1018.5eV to 1020eV and the zenith angle of primary cosmic ray particles from 0 to 45 for proton and iron primaries. We have compared the results from CORSIKA and COSMOS. The comparison has shown perceptible differences in the ground distributions, longitudinal distributions, Calorimetric energy, and Xmax distributions. We have also measured the detector response evaluated using GEANT4 simulations. Here, we discuss S(800), i.e. the signal at a distance of 800 m from the shower core, as the primary energy estimator and present the lateral distribution function(LDF) with S(800).

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.36.3-36.3
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• 2017

The Telescope Array (TA) experiment reported the arrival direction distribution of ultra-high-energy cosmic rays (UHECRs) with energies above $5.7{\times}10^{19}eV$ in the northern sky. A clustering of TA events, the so-called hotspot, was found; however, its nature has not yet been understood. To understand the origin of the TA hotspot, we examine the sky distributions of the TA UHECR arrival direction and filamentary structures of galaxies in the local universe. By statistical tests for anisotropy, we find a close correlation of the TA events with the filaments of galaxies connected to the Virgo cluster. We discuss our finding and its implications.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.421-426
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• 2004

I briefly review the current theoretical status of the origins of ultrahigh energy cosmic rays with special emphasis on models associated with galaxy clusters. Some basic constraints on models are laid out, including those that apply both to so-called 'top-down' and 'bottom-up' models. The origins of these UHECRs remain an enigma; no model stands out as a clear favorite. Large scale structure formation shocks, while very attractive conceptually in this context, are unlikely to be able to accelerate particles to energies much above $10^{18}eV$. Terminal shocks in relativistic AGN jets seem to be more viable candidates physically, but suffer from their rarity in the local universe. Several other, representative, models are outlined for comparison.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.111-121
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• 2003

In order to explore the cosmic ray acceleration at the cosmological shocks, we have performed numerical simulations of one-dimensional, plane-parallel, cosmic ray (CR) modified shocks with the newly developed CRASH (Cosmic Ray Amr SHock) numerical code. Based on the hypothesis that strong Alfven waves are self-generated by streaming CRs, the Bohm diffusion model for CRs is adopted. The code includes a plasma-physics-based 'injection' model that transfers a small proportion of the thermal proton flux through the shock into low energy CRs for acceleration there. We found that, for strong accretion shocks with Mach numbers greater than 10, CRs can absorb most of shock kinetic energy and the accretion shock speed is reduced up to $20\%$, compared to pure gas dynamic shocks. Although the amount of kinetic energy passed through accretion shocks is small, since they propagate into the low density intergalactic medium, they might possibly provide acceleration sites for ultra-high energy cosmic rays of $E\ll10^{18}eV$. For internal/merger shocks with Mach numbers less than 3, however, the energy transfer to CRs is only about $10-20\%$ and so nonlinear feedback due to the CR pressure is insignificant. Considering that intracluster medium (ICM) can be shocked repeatedly, however, the CRs generated by these weak shocks could be sufficient to explain the observed non-thermal signatures from clusters of galaxies.

• Publications of The Korean Astronomical Society
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• v.21 no.2
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• pp.87-94
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• 2006

The COREA (COsmic ray Research and Education Array in Korea) project aims to build a ground array of particle detectors distributed over Korean Peninsular, through collaborations of high school students, educators, and university researchers, in order to study the origin of ultra high energy cosmic rays. COREA array will consist of about 2000 detector stations covering several hundreds of $km^2$ area at its final configuration and detect electrons and muons in extensive air-showers triggered by high energy particles. During the intial phase COREA array will start with a small number of detector stations in Seoul area schools. In this paper, we have studied by Monte Carlo simulations how to select detector sites for optimal detection efficiency for proton triggered air-showers. We considered several model clusters with up to 30 detector stations and calculated the effective number of air-shower events that can be detected per year for each cluster. The greatest detection efficiency is achieved when the mean distance between detector stations of a cluster is comparable to the effective radius of the air-shower of a given proton energy. We find the detection efficiency of a cluster with randomly selected detector sites is comparable to that of clusters with uniform detector spacing. We also considered a hybrid cluster with 60 detector stations that combines a small cluster with ${\Delta}{\iota}{\approx}100m$ and a large cluster with ${Delta}{\iota}{\approx}1km$. We suggest that it can be an ideal configuration for the initial phase study of the COREA project, since it can measure the cosmic rays with a wide range energy, i.e., $10^{16}eV{\leq}E{\leq}10^{19}eV$, with a reasonable detection rate.

• The Bulletin of The Korean Astronomical Society
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• v.34 no.1
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• pp.62.2-62.2
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• 2009

• Bulletin of the Korean Space Science Society
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• 2009.04a
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• pp.34.4-35
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• 2009

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.549-552
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• 2015

The galactic magnetic field (GMF) and the intergalactic magnetic field (IGMF) affect the propagation of ultra-high energy cosmic rays (UHECRs) from the source to us. Here we examine the influences of the GMF/IGFM and the dependence of their sky distribution on galactic latitude, b. We analyze the correlation between the arrival direction (AD) of UHECRs observed by the Pierre Auger Observatory and the large-scale structure of the universe in regions of sky divided by b. Specifically, we compare the AD distribution of observed UHECRs to that of mock UHECRs generated from a source model constructed with active galactic nuclei. Our source model has the smearing angle as a free parameter that reflects the deflection angle of UHECRs from the source. The results show that larger smearing angles are required for the observed distribution of UHECRs in lower galactic latitude regions. We obtain, for instance, a $1{\sigma}$ credible interval for smearing angle of $0^{\circ}{\leq}{\theta}_s{\leq}72^{\circ}$ at high galactic latitudes, $60^{\circ}$ < $\left|{b}\right|{\leq}90^{\circ}$, and of $75^{\circ}{\leq}{\theta}_s{\leq}180^{\circ}$, $-30^{\circ}{\leq}b{\leq}30^{\circ}$, at low galactic latitudes, respectively. The results show that the influence of the GMF is stronger than that of the IGMF. In addition, we can estimate the strength of GMFs by these values; if we assume that UHECRs would have heavier nuclei, the estimated strengths of GMF are consistent with the observational value of a few ${\mu}G$. More data from the future experiments may make UHECR astronomy possible.