1. 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

2. 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

3. 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

4. Observation Detection of EAS Surface Detector (SD) – e, ¹
Fluorescence Detector (FD) - UVL
Cherenkov Radiation
Radio wave
Radar reflection
Longitudinal development
Lateral distribution

5. 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

6. 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

7. JEM-EUSO (planned)

8. 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

9. 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.

10. 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

11. 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

12. 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

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

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

15. 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

16. 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

17. 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

18. 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.

19. 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

20. RA, DEC Distribution 2D Distribution 1D Distribution
Observed Data (TA, E≥1 EeV)
Simulation Data (Isotropic)
1D Distribution
RA Distribution
DEC Distribution

21. Auto-Angular Distance Distr. (AADD)
Caution: AADD is not an independent sampling. Probability(D) must be obtained from simulation.
clustered
isotropic

22. Correl. Angular Distance Distr. (CADD)
H.B.K, J. Kim, JCAP 1103, 006 (2011)
correlated
isotropic

23. 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

24. Super-Heavy Dark Matter (SHDM) Model
Unfavorable

25. 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

26. 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

27. 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

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

29. 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)

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

31. 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

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

33. Cen A as a UHECR source Incorporation of Void structure
H.B.K, JKPS 62, 708 (2013)

34. 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

35. 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).

36. 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.

37. 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?

38. 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