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**Search for the Ultra High Energy Cosmic Ray Sources : the Current Status**

Hang Bae Kim (HanYang University) High KIAS-NCTS Joint Workshop on Particle Physics, String Theory and Cosmology February 12, 2014

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**Ultra-High-Energy Cosmic Rays**

High energy particle from outer space Primarily composed of proton & nuclei Originated from SNe, AGN, … ? Influence on the life Ultra-High Energy Cosmic Ray (UHECR) Energy : 1962, E>1020 eV at Vocano Ranch 1991, E=3£1020 eV at Fly’s eye (OMG particle) ~ kinetic energy of a baseball with a speed of 100 km/h Extensive Air Shower (EAS) Extragalactic origin Where and How can particles reach such extremely high energies? 1 particle/km2/century

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Production Acceleration of charged particles Decay of superheavy particles Propagation Cosmic background (Microwave, Radio wave, Magnetic fields) Energy loss Secondary CR production Deflection and Time lag Observation Atmosphere as calorimeter / scintillator Composition Energy Arrival Direction

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**Observation Detection of EAS Surface Detector (SD) – e, ¹**

Fluorescence Detector (FD) - UVL Cherenkov Radiation Radio wave Radar reflection Longitudinal development Lateral distribution

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**Pierre Auger Observatory (PAO)**

Surface Detector – Water Cherenkov 60 km Fluorescence Detector – PMT Location : Mendoza, Argentina SD : 1600 water Cherenkov detector, km spacing, 3000 km2 FD : 24 telescopes in 4 stations

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**Telescope Array (TA) Location : Utah, USA**

Surface Detector – Plastic Scintillation 35km SD array FD station MD LR BRM Fluorescence Detector – PMT Location : Utah, USA SD : 507 plastic scintillation detector, km spacing, 678 km2 FD : 18 telescopes in 3 stations

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JEM-EUSO (planned)

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**Energy, Arrival Direction**

Surface Detector Signal & Timing Lateral distribution S(1000) Good energy estimator Distance from the shower axis Energy Calibration through hybrid events Fluorescence Detector Longitudinal development

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**Composition Longitudinal development Xmax, depth of shower maximum**

atmospheric depth Shower maximum Xmax, depth of shower maximum Xmax, the depth of shower maximum depends on energy and composition of primary CR particle. Average longitudinal development of proton and Fe nucleus obtained from simulation. Proton has larger X_{max} than Fe. Observed variation of Xmax as a function of energy.

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**Injected spectrum ! Observed spectrum**

Propagation Energy Loss UHECR p, A, γ interact with CMB photons. The energy of protons as a function of the propagation distance. Modification factor of energy spectrum Injected spectrum ! Observed spectrum

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**Propagation Deflection Magnetic fields ! Deflection and Time lag**

Galactic magnetic field BG ~ 10-6 G RG~10 kpc Extragalactic magnetic field BEG ~ 10-9 – 10-6 G (very uncertain) Proton propagation in a magnetic field of 10-9G

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Production Top-down : Decay of superheavy particles, Emission from Topological defects Superheavy particle with long lifetime Emission from topological defects Cosmic origin involves new (cosmology + particle physics) Signatures of top-down models Spectral shape – No GZK cutoff, flat spectrum Composition – Neutrinos and photons are dominant Arrival Directions – Galactic anisotropy

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Production Bottom-up : Acceleration of charged particle at astrophysical sites Maximum attainable energy Acceleration mechanism Diffusive shock acceleration Acceleration site AGN, GRB, …

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**Latest Results and Issues**

Energy spectrum Abu-Zayyad et al. (2013) 1990s, AGASA reported No GZK cutoff. HiRes, Auger, TA confirmed GZK cutoff.

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**Latest Results and Issues**

Composition HiRes (Abbasi et al. 2010) PAO (Abraham et al. 2010) TA (Tameda et al. 2011) PAO : Transition from proton to heavy nuclei - Ad hoc composition model (p, He, N, Fe) HiRes & TA : Proton

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**Latest Results and Issues**

Arrival directions AGASA (Hayashida et al. 2000) HiRes (Abbasi et al. 2008) AGASA - Isotropy with small clustering TA (Abu-Zayyad et al. 2012) PAO (Abreu et al. 2010) Auger Anisotropy Correlation with AGNs Low (<10^{19} eV) energy isotropy Above GZK cutoff, anisotropy confirmed PAO – Correlation with AGN

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**Study of Arrival Directions**

Experiment Modeling Observed AD distribution Expected AD distribution Statistical Comparison Probability that the observed distribution is obtained from the expected distribution Test Methods - Statistic Multipole moments, 2D KS, … KS on the reduced 1D distribution Isotropy Astrophysical Objects Simulation

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Exposure Function The detector array does not cover the sky uniformly and we must consider its efficiency as a function of the arrival direction. Here we consider only the geometrical efficiency.

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**Kolmogorov-Smirnov Test**

Comparison of two one-dimensional distributions Kolmogorov-Smirnov statistic Cumulative probability distribution KS statistic Kuiper statistic Probability that the observed distribution is obtained from the expected distribution Anderson-Darling statistic

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**RA, DEC Distribution 2D Distribution 1D Distribution**

Observed Data (TA, E≥1 EeV) Simulation Data (Isotropic) 1D Distribution RA Distribution DEC Distribution

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**Auto-Angular Distance Distr. (AADD)**

Caution: AADD is not an independent sampling. Probability(D) must be obtained from simulation. clustered isotropic

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**Correl. Angular Distance Distr. (CADD)**

H.B.K, J. Kim, JCAP 1103, 006 (2011) correlated isotropic

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**Super-Heavy Dark Matter (SHDM) Model**

UHECR flux is obtained by the line-of-sight integration of the UHECR luminosity function L(R), which is proportional to the DM density ρ(R). Galactic DM contribution / Extragalactic DM contribution Galactic DM contribution UHECR Luminosity Dark Matter Profile

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**Super-Heavy Dark Matter (SHDM) Model**

Unfavorable

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**AGN Model Hypothesis : UHECRs are composed of**

H.B.K, J. Kim, JCAP 1103, 006 (2011) IJMPD 22, (2013) Hypothesis : UHECRs are composed of AGN contribution, fraction fA Background (isotropic) contribution, fraction 1-fA Selection of UHECR data Energy cut We take Selection of AGN Distance cut Notes The fraction f depends on Ec and dc. PAO-AGN

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AGN Model UHECR flux from AGN For simplicity, we assume the universality of AGN. Expected flux AGN contribution fraction fA, Isotropic component fraction 1-fA, UHECR Luminosity Distance Smearing

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AGN Model Steep rise of CPD near µ=0 means the strong correlation at small angles. PAO data are not consistent with isotropy, meaning that they are much more correlated with AGNs than isotropic distribution. PAO data are not consistent either with the hypothesis that they are completely from AGNs. Adding isotropic component can make the consistency improved. The cumulative probability distribution of CADD using the AGN reference set

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AGN Model PAO Consistent with the simple AGN model when enough isotropic component is added. Cf. Fiducial value of f

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**Point-wise Anisotropy**

Excess Deficit Idea – Sweep the whole sky and perform the point-wise comparison to the isotropic distribution (Comparison method: CADD with a point reference) Features of PAO AD anisotropy One prominent excess region around Centaurus A One void region near the south pole H.B.K MPLA 28, (2013)

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Hot spot ? Features of TA AD anisotropy No prominent excess region Broad hot spot One void region near the north pole

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Cen A as a UHECR source H.B.K, ApJ 764, 121 (2013) Centaurus A is a nearby strong source of radio waves to γ-rays. The PAO data show the clustering of UHECRs around Centaurus A. M87 Centaurus A Modeling Centaurus A as a point source of UHECRs Centaurus A contribution + Isotropic background the Cen A fraction the smearing angle

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Cen A as a UHECR source Among 69 UHECR observed by PAO, about 10 (6 ~ 17) UHECR can be attributed to Cen A contribution.

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**Cen A as a UHECR source Incorporation of Void structure**

H.B.K, JKPS 62, 708 (2013)

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**Centaurus A – a UHECR source**

Estimate of intergalactic magnetic fields from the deflection angles By using UHECRs around Centaurus A, the estimate of IGMF is Without voids – 10 UHECRs With voids – 18 UHECRs

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**Composition and GMF Influence**

GMF model – Prouza-Smida (2003) model Fit to observed Faraday rotations Disk field Toroidal field Poloidal field The Galactic plane section of the disk field of the PS model Lorentz force equation The deflection map of UHECR in the PS model for Z=1 (proton).

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**Composition and GMF Influence**

H.B.K, JKPS 63, 135 (2013) The deflections of arrival directions of 69 UHECRs detected by the PAO, due to the GMF, computed using the PS model, when UHECRs are protons (Left), or iron nuclei (Right). Red circles mark the arrival directions detected at the earth, and black bullets connected by yellow lines mark the arrival directions before UHECR enter the GMF .The blue square marks the direction of Centaurus A. If all UHECRs are protons, the clustering around Centaurus A is not altered significantly. If all UHECRs are iron nuclei, the clustering around Centaurus A may be a fake due to the GMF.

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Summary After 100 years of research, the origin of cosmic rays is still an open question, with a degree of uncertainty increasing with energy. Statistically meaningful data have been accumulated, but not yet conclusive about composition and arrival directions. Statistical methods to compare two distributions of UHECR arrival directions. 2D → 1D reduction : CADD KS or KP test Point-wise anisotropy and point source search Centaurus A seems to be a strong source of UHECRs. Estimate of IGMF : The influence of GMF may tell something about composition. Beginning of cosmic ray astronomy?

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**New Window to the sky Tycho’s Mural quadrant Galileo’s telescope**

Herschel’s telescope Hubble’s telescope Jansky’s radio antenna Penzias & Wilson’s antenna Hubble Space Telescope Planck satellite Chandra X-ray telescope

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