Ultra-High Energy Cosmic Rays and Astrophysics Hang Bae Kim Hanyang University Hangdang Workshop, 2012. 08. 22
Ultra High Energy Cosmic Rays Ultra High Energy Cosmic Ray (UHECR)» E 3 E & 10 18 ev Energy : 1962, >10 20 ev at Vocano Ranch 1991, 3 10 20 ev at Fly s eye (OMG particle) ~ kinetic energy of a baseball with a speed of 100 km/h Extensive Air Shower (EAS) 1 particle/km 2 /century Extragalactic origin Where and How particles reach such extremely high energies?
Production Acceleration of charged particles Decay of superheavy particles Propagation Cosmic background Microwave, Radiowave, Magnetic fields Energy loss Secondary CR production Deflection and Time lag Observation Atmosphere as calorie meter/scintillator Composition Energy Arrival Direction
Observation Detection of EAS Surface Detector (SD) e, ¹ Fluorescence Detector (FD) - UVL Cherenkov Radiation Radiowave Longitudinal development Lateral distribution
60 km Pierre Auger Observatory (PAO) Surface Detector Water Cherenkov Fluorescence Detector PMT Location : Mendoza, Argentina SD : 1600 water Cherenkov detector, 1.5 km spacing, 3000 km 2 FD : 24 telescopes in 4 stations
Telescope Array (TA) MD FD station Surface Detector Plastic Scintillation BRM SD array LR Fluorescence Detector PMT 35km Location : Utah, USA SD : 507 plastic scintillation detector, 1.2 km spacing, 678 km 2 FD : 18 telescopes in 3 stations
JEM-EUSO
Energy, Arrival Direction Surface Detector Signal & Timing Lateral distribution Good energy estimator S(1000) Energy Calibration through hybrid events Fluorescence Detector Distance from the shower axis Longitudinal development
Composition Longitudinal development Shower maximum X max, depth of shower maximum atmospheric depth X max, 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 X max as a function of energy.
Propagation Energy Loss UHECR p, A, γ interact with CMB photons. N +! N + ¼ (photo-pion production) E t h ¼ 6:8 10 19 E B =10 3 ev 1 ev (threshold energy) E GZK ¼ 4 10 19 ev The energy of protons as a function of the propagation distance. Modification factor of energy spectrum Injected spectrum! Observed spectrum
Propagation Deflection Magnetic fields! Deflection and Time lag µ 1 µ µ ±µ = 0:52 ± E d B Z 10 20 ev 1Mpc 10 9 G Galactic magnetic field B G ~ 10-6 G R G ~10 kpc Extragalactic magnetic field B EG ~ 10-9 10-6 G (very uncertain) Proton propagation in a magnetic field of 10-9 G
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
Production Bottom-up : Acceleration of charged particle at astrophysical sites Maximum attainable energy E max ¼ µ B G µ R 1pc ZeV Acceleration mechanism Diffusive shock acceleration Acceleration site Active galactic nuclei (AGN)
Latest Results and Issues Energy spectrum 1990s, AGASA reported No GZK cutoff. HiRes & Auger confirms GZK cutoff.\ Ankle and Dip problem
Latest Results and Issues Composition HiRes : Proton PAO : Transition from proton to heavy nuclei
Latest Results and Issues Arrival directions AGASA Isotropy with small clustering Auger Anisotropy Correlation with AGNs
Arrival Direction Analysis Experiment Dark Matter Decay Astrophysical Objects Modeling Simulation Observed AD distribution Expected AD distribution Statistical Comparison Test Methods Multipole moments 2D KS KS on the reduced 1D distribution Probability that the observed distribution is obtained from the expected distribution
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. Arrival Direction : ( ; ±) (Right Ascension, Declination) Detector Geometry : (Lattitude); µ m (Zenith angle cut) h(±) = 1 ¼ [sin m cos cos± + m sin sin ±] m = 8 < : 0; for» > 1; ¼; for» < 1; cos 1»; otherwise» = cosµ m sin sin ± cos cos± PAO : = 35:20 ± ; µ m = 60 ± AGASA : = + 35:78 ± ; µ m = 45 ±
Kolmogorov-Smirnov Test Comparison of two one-dimensional distributions Kolmogorov-Smirnov statistic Cumulative probability distribution S N (x) = 1 N KS statistic X N i = 1 µ(x i x) D = max js N 1 (x) S N 2 (x)j Probability that the observed distribution is obtained from the expected distribution Probability(D > observed) = Q K S ³hp Ne + 0:12 + 0:11= p N e i D 1X Q K S ( ) = 2 ( 1) j 1 e 2j 2 2 j = 1 N e = N 1 N 2 N 1 + N 2
Auto-Angular Distance Distr. (AADD) AD dist. : f ^r i j i = 1; : : : ; N g AADD : f cosµ i j ^r i ^r j j i; j = 1; : : : ; N g clustered isotropic
Correl. Angular Distance Distr. (CADD) AD distr. : f ^r i j i = 1; : : : ; N g Reference directions : f ^r 0 j j j = 1; : : : ; M g CADD : f cosµ i j 0 ^r i ^r 0 j j i = 1; : : : ; N ; j = 1; : : : ; M g correlated isotropic
Flux-Exposure Value Distr. (FEVD) AD distr. : f ^r i j i = 1; : : : ; N g Expected Flux : f (^r) FEVD : f F i f (^r i )h(^r i ) j i = 1; : : : ; N g flux-following isotropic
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 ½ G R G =½ DM R GZK ¼ 10 5 10 4 ¼ 10 Galactic DM contribution f DM (µ) = 1 4¼ Z r m ax 0 L µ q r 2 2r R 0 cosµ + R 2 0 dr UHECR Luminosity Decay : L(R) / n DM (R) / ½ DM (R) Dark Matter Profile ½ I T (R) / ½ NFW (R) / 1 R 2 + Rc 2 1 R(R 2 + Rs) 2 cosµ = cosbcosl
Super-Heavy Dark Matter (SHDM) Model Ruled out!
Simple AGN Model Hypothesis : UHECRs are composed of AGN contribution, fraction f A Background (isotropic) contribution, fraction 1-f A Selection of UHECR data Energy cut We take Selection of AGN Distance cut We take E E c E GZK d d c ¼ r GZK d c = 100Mpc Notes The fraction f depends on E c and d c. PAO-AGN
UHECR flux from AGN Simple AGN Model UHECR Luminosity Distance Smearing For simplicity, we assume the universality of AGN. Expected flux AGN contribution fraction f A, Isotropic component fraction 1-f A, / f AGN (^r)h(^r) / h(^r)
Simple AGN Model The cumulative probability distribution of CADD using the AGN reference set 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.
Simple AGN Model PAO Consistent with the simple AGN model when enough isotropic component is added. Cf. Fiducial value of f ½ Ec = 5:7 10 f ¼ 0:7 for 19 ev d c = 100Mpc
Anisotropy Pointwise Excess Deficit
Centaurus A Centaurus A is a nearby strong source of radio-wave, γ-ray,
Centaurus A Among 69 UHECR observed by PAO, about 10 (6 ~ 17) UHECR can be attributed to Cen A contribution. Estimate of intergalactic magnetic fields
Summary After 100 years of research, the orgin 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: composition, energy spectrum, arrival directions. We develop new statistical methods to compare two distributions of UHECR arrival directions. 2D 1D reduction: CADD, AADD, FEVD KS, KP test PAO/SUGAR data disfavor the SHDM model for UHECR. PAO data : inconsistent with isotropy, some correlation with AGN Centaurus A seems to be a strong source of UHECR Beginning of cosmic ray astronomy?