Reference:	Abbasi, R.U., et al., ApJL, 790, L21	Published July 2014

Highest-Energy
Cosmic-Ray Hotspot Observedby the Telescope Array Experiment
Kazumasa Kawata
ICRR, University of Tokyo
For the Telescope Array Collaboration1

29 institutions, 126 members

Telescope Array Collaboration
R.U. Abbasi1, M. Abe13, T.Abu-Zayyad1, M. Allen1, R. Anderson1, R. Azuma2, E. Barcikowski1, J.W. Belz1,D.R. Bergman1, S.A. Blake1, R. Cady1, M.J. Chae3, B.G. Cheon4, J. Chiba5, M. Chikawa6, W.R. Cho7, T. Fujii8,
M. Fukushima8,9, T. Goto10, W. Hanlon1, Y. Hayashi10, N. Hayashida11, K. Hibino11, K. Honda12, D. Ikeda8,N. Inoue13, T. Ishii12, R. Ishimori2, H. Ito14, D. Ivanov1, C.C.H. Jui1, K. Kadota16, F. Kakimoto2, O. Kalashev17,
K. Kasahara18, H. Kawai19, S. Kawakami10, S. Kawana13, K. Kawata8, E. Kido8, H.B. Kim4, J.H. Kim1, J.H. Kim25,
S. Kitamura2, Y. Kitamura2, V. Kuzmin17, Y.J. Kwon7, J. Lan1, S.I. Lim3, J.P. Lundquist1, K. Machida12, K. Martens9,T. Matsuda20, T. Matsuyama10, J.N. Matthews1, M. Minamino10, K. Mukai12, I. Myers1, K. Nagasawa13,
S. Nagataki14, T. Nakamura21, T. Nonaka8, A. Nozato6, S. Ogio10, J. Ogura2, M. Ohnishi8, H. Ohoka8, K. Oki8,
T. Okuda22, M. Ono14, A. Oshima10, S. Ozawa18, I.H. Park23, M.S. Pshirkov24, D.C. Rodriguez1, G. Rubtsov17,
D. Ryu25, H. Sagawa8, N. Sakurai10, A.L. Sampson1, L.M. Scott15, P.D. Shah1, F. Shibata12, T. Shibata8,H. Shimodaira8, B.K. Shin4, J.D. Smith1, P. Sokolsky1, R.W. Springer1, B.T. Stokes1, S.R. Stratton1,15, T.A. Stroman1,T. Suzawa13, M. Takamura5, M. Takeda8, R. Takeishi8, A. Taketa26,M. Takita8, Y. Tameda11, H. Tanaka10,
K. Tanaka27, M. Tanaka20, S.B. Thomas1, G.B. Thomson1, P. Tinyakov17,24, I. Tkachev17, H. Tokuno2, T. Tomida28,
S. Troitsky17, Y. Tsunesada2, K. Tsutsumi2, Y. Uchihori29, S. Udo11, F. Urban24, G. Vasiloff1, T. Wong1, R. Yamane10,H. Yamaoka20, K. Yamazaki10, J. Yang3, K. Yashiro5, Y. Yoneda10, S. Yoshida19, H. Yoshii30, R. Zollinger1, Z. Zundel1
1 University of Utah 2 Tokyo Institute of Technology 3 Ewha Womans University 4 Hanyang University
5 Tokyo University of Science 6 Kinki University 7 Yonsei University 8 ICRR, University of Tokyo
9 IPMU, the University of Tokyo 10 Osaka City University 11 Kanagawa University 12 University of Yamanashi
13 Saitama University 14 Astrophysical Big Bang Laboratory RIKEN, Wako 15 Rutgers University
16 Tokyo City University17 INR of the Russian Academy of Sciences 18 Waseda University19 Chiba University 20 KEK 21 Kochi University 22 Ritsumeikan University 23 Sungkyunkwan University
24 Universite de Libre de Bruxelles 25 Ulsan National Institute of Science and Technology
26 ERI, University of Tokyo 27 Hiroshima City University 28 Advanced Science Institute, RIKEN
29 National Institute of Radiological Science 30 Ehime University2

Outline• Highest-Energy Cosmic Ray• Telescope Array Experiment• Hotspot Analysis & Result+ New 1-year result• Discussions• Summary & Future Prospects

3

Highest-Energy Cosmic RayKnee

SNR

2nd-Knee?

Ankle

SNR?
Matthiae, New J. Phys. (2010)

Highest-E
Cosmic Rayv Cosmic rays
Power-law spectrum
in wide energy rangev Origin of cosmic ray up to 1014eV- SNRs in our Galaxy
GeV-TeV observations gavesome indirect evidencesof the proton accelerationv 1014eV – 1019eV(Knee - Ankle)- Index changes- Composition changing- Galactic objects?
v Highest-E cosmic rays
around 1020eV- Flux suppression- Extragalactic (AGNs?)- 1 particle/100km2/ year4

Hillas Diagramv Larmor Radius RL
neutron star

protoFewhitedwarf

n=100kpc Z-1 (µG/B)(E/100EeV)>> galactic disk

10 20eV10 20eVv Source should have capabilityof confining particle up to EMAXAGNAGN jets
GRB

hot spots
SNR
IGM shocks
Galaxy cluster

11:

Kotera & Olinto, Annu. Rev. Astron. Astrophys (2010)v Necessary condition,
but not sufficientv EMAX depends on
acceleration mechanismv Recent simulations
relativistic shocks in AGN can’t
accelerate up to 1020eV?

d Hillas (1984) diagram. Above the blue (red) line protons (iron nuclei) can be confined tomum energy of Emax = 1020 eV. The most powerful candidate sources are shown with thenties in their parameters.

5Motivation

Search forViolent
Accelerator
in the Universe

Energetic jets of active galaxy（Centaurus A）
ESO/WFI (visible); MPIfR/ESO/APEX/A.Weiss et al. (microwave); NASA/CXC/CfA/R.Kraft et al. (X-ray)）

Search for

Motivation

Violent
Accelerator
in the Universe

Jets(R=~kpc)

AGN
Super-massive BH
Accretion disk & torus(R=~pc)Lobe(R>~10kpc)

Hot Spot(R=~kpc)

Energetic jets of active galaxy（Centaurus A）
ESO/WFI (visible); MPIfR/ESO/APEX/A.Weiss et al. (microwave); NASA/CXC/CfA/R.Kraft et al. (X-ray)）

Search forViolent
Accelerator
in the Universe
Gamma Ray Burst
Artist view (ES0)Colliding clusters of galaxies
STScI, U. Arizona, CfA, CXC, NASAWhy highest energy cosmic rays?
Cosmic rays are charged particles

Cosmic rayOrigin

Highest cosm

ic raysv Low energy cosmic raysà bend by the magnetic fieldà Isotropy at the Earthv Highest energy cosmic raysà Almost go straight against magnetic fieldà Possible to find cosmic-ray origin directly9Outline• Highest-Energy Cosmic Ray• Telescope Array Experiment• Hotspot Analysis & Result• Discussions• Summary & Future Prospects

10What do we see?

astro.uchicago.edu/cosmus/projects/aires(Simulated by AIRES)

Detect Air Showerin the atmosphere
When cosmic ray interact
with nuclei in atmosphere,
many secondary particles
are generated.
² A highest-E cosmic ray makes
more than 100 billion particles.
² Air shower expand acrossa few km on the ground11

Two Different Type
Detectors

Xmax
Tec
Detect fluorescence lights emitted
fromnitrogen excited by• air-shower
particles
Shower longitudinaldevelopment••

depends on primary particle type.
FD observes shower development
directly.
Xmax is the most efficientparameter for determining
primaryparticletype.
Masscompsition

Iron / Proton

Depth [g/cm2]

Surface Particle
Detector
SD : Regardless of weather condition with high duty circle and wide FoV.
à High statistical data à Anisotropy & spectral shape
FD : limited to clear moonless night.
Longitudinal development of air shower à Mass composition (Xmax)
Measure the energy deposit calorimetrically à Absolute energy scale

GroundXmaxSkyFluorescence
DetectorNumber of charged particle

Shower longitudinal development

12

Telescope Array Experimentv Desert in Utah, USA- 39.30°N, 112.91°W

32kmv Surface Particle Detector (SD)
- 3m2 Scintillation Detector- 507 det. With 1.2km spacing- Distributed across 700km2v Fluorescence Detector (FD)
- 3 stations- 12 telescopes / station

28km

13

Telescope Array Experimentv Desert in Utah, USA- 39.30°N, 112.91°Wv Surface Particle Detector (SD)
- 3m2 Scintillation Detector- 507 det. With 1.2km spacing- Distributed across 700km2~Tokyo 23 wardsv Fluorescence Detector (FD)
- 3 stations- 12 telescopes / station

14

Detect fluorescence lights emitted fromnitrogen excited by air-shower particles

Communication
Antenna

Solar panel（1m×1m）
700km2 (Tokyo 23 wards)
with 1.2km spacing- 2 layer Scintillators+ WLS fibers + 2PMTs- DAQ 50MHz FADC
- Solar power system- Communication antennaà Stand-alone detector 16

Scintillator
DAQ records
signal size & timing

Recorded Air Shower EventNorthW

E

3km
５km
SUpper view

Side view

Radius : Signal size à Cosmic ray energy
Color : Signal timing Blueà Early RedàLateà Cosmic ray direction18

Outline• Highest-Energy Cosmic Ray• Telescope Array Experiment• Hotspot Analysis & Result• Discussions• Summary & Future Prospect

19

SD Data Setv Period :2008 May – 2013 May (5 years)v Cut conditions :- # of used detectors >=4- Zenith angle < 55°- Energy > 57EeV(which corresponds to the energy
determined by the AGN correlation
analysis by the Auger group in 2007)- No boundary cut(increase +20 events,but worsen E & angular resolutions)

Resolutions

InnerOuterAngular

1.0°

1.7°

Energy15%20%

à Good enough to search forintermediate-scale anisotropy

OuterInner= 72 events
20

Directions of Cosmic Rays

GalacticCenterSupergalacitc
Plane

Equatorial Coordinate

Field of View

72 TA events on the equatorial coordinate
Full event table is available in the ApJL online journal :http://iopscience.iop.org/2041-8205/790/2/L21/suppdata/apjl498370t1_mrt.txt

21

Events Summed Over 20°-radius-circle
Equatorial Coordinate

Maximum excess = 1920°-radius circle was used for intermediate-scale anisotropy searcharound 1EeV by the AGASA, HiRes and TA. (Kawata et al. 2013 ICRC)

22

Isotropic Sky Background(Events Summed Over 20°-radius-circle)
Equatorial Coordinate

B.G at Dec 40° = ~4.5

By the MC simulation assuming TA geometrical exposure

23Data/MC Comparison(>10EeV)
MC simulation was verified
by high-statistics control sample (>10EeV)

Data
MC

Data
MC

24

Deficit

Ave.

ExcessSignificance Map 5 years

Found cosmic ray “hotspot” at speciﬁc regionà Max Signiﬁcance 5.1σ at R.A.=146.7 , Dec.=43.2

25

Chance Probability
Random 72 eventsassuming isotropy(TA geometrical exposure)

5.1σ

Adopt same analysis &create significance maps
(by five oversampling radius: 15, 20, 25, 30, 35 deg.)

Search for maximum
significance in the FoV

Repeat 1 million times
How many >5.1σ ?

P = 371 / 1,000,000 trials= 3.7 x 10-4 (3.4σ)

26

6-Year Data by TA

Out of FoV

5-year data
New 1-year data

Our FoV (Dec>-10°)
Definition in ApJL

Period:2008 May 11 – 2014 May 11 (87 events)

27

Significance Map 6 years
Oversampling with 20°-radius circle

Max significance 5.55σ (Non = 23, Nbg=5.49)
Centered at R.A=148.4°, Dec.=44.5° (shifted from SGP by 17°)
Chance probability of appearing in isotropic sky à 4.0σ	

28

Outline• Highest-Energy Cosmic Ray• Telescope Array Experiment• Hotspot Analysis & Result• Discussions• Summary & Future Prospects

29

What is the Origin?

30

33
IC TA
R SD
CSpectrum Measured
by
ND NTERNATIONALOSMIC

ONFEREN>57 EeVSD Spectrum

JE (eV 2 m2 s sr)-11025

JE (eV 2 m2 s sr)-11025

Suppression isobserved at5.5σ
3TA Experiment3Cosmic Ray Flux ｘE３

AY10241024

γ 1 = -3.34(4)γ = -3118log (EEankle = 4.6(3)× 10 eV
γ 2 = -2.67(3)10γ = -2219log (EEGZK = 5.4(3)× 10 eV
γ = -4.6(6)10γ = -43181018.2

1818.418.6

18.8

31919.2

1919.4

19.6

10Energy E (eV)

19.8

20

1020.220.4log (E /eV)
2010Fig. 1: The spectrum of cosmic rays as measured by theOnedetectorof interpretations: GZKsurfaceof TA [1]. A broken powerlaw eﬀect
fit to thedata is also shown.

1818.2

Fig. 2: The s
FADC fluore
fit to the data
31

GZK EffectCosmic Background
Radiation(CMB)

Highest-E cosmic ray
Highest energy regionv Highest-E cosmic ray travel beyond 50Mpc
rapidly loss their energy by interaction with the cosmic microwave
background. à Greisen-Zatsepin-Kuzmin (GZK) EffectHighest-E cosmic rays can not reach the Earthfrom the distant universe. Therefore, Origin ofcosmic rays should be limited to local universe
32

Galaxy Distribution in Local Universe
Large-Scale Structure(LSS)

2MASS catalog velocity 0 – 3000 km/s
John P. Huchra, et al 2012, ApJ, 199, 26
à high completeness catalog

Supergalactic Plane(SGP)

Heliocentric velocity (Rough Distance)
Red:0-1000km/s (D = 0-15Mpc)
Blue: 1000-2000km/s (D = 15-30Mpc)
Green: 2000-3000km/s (D = 30-45Mpc)
33

Nearby Galaxy Clusters
Ursa Major Cluster(D=20Mpc)
Virgo Cluster(D=20Mpc)

2MASS catalog velocity 0 – 3000 km/s
John P. Huchra, et al 2012, ApJ, 199, 26+ 5-year TA data (Color contour)

Perseus-PiscesSupercluster(D=70Mpc)

Heliocentric velocity (Rough Distance)
Red:0-1000km/s (D = 0-15Mpc)
Blue: 1000-2000km/s (D = 15-30Mpc)
Green: 2000-3000km/s (D = 30-45Mpc)
34

Nearby Prominent AGNs
Dermer, et al., arXiv:0811.1160

Ursa Major
Cluster (20Mpc)
Mrk180
1ES J1959+65
BL LacM106

Cyg A
Mrk501

M81
M82

Perseus-PiscesSupercluster (70Mpc)

3C66B

Mrk421

Virgo Cluster(20Mpc)

RGB J0152+017

Cen A
Tully Local Void

TA : 2008 May – 2014 May (6.0 years) 87 events
Auger : 2004 May – 2009 Nov (5.5 years) 62 events

35

IceCube Neutrino

Fang, Fujii, Linden & Olinto, arXiv:1404.6237

UHECRs + photons à TeV-PeV Neutrinos
80TA hotspot

60Dec. [deg]603040IceCube
ν > 30TeV(Circle size:Ang. Resol.)

20
0360

180

0R.A. [deg]-20-40-30-60-80

-60
-150

-100-50

050

100

150

Two IceCube neutrinos among northern 4 events arecoincident with the TA hotspot. à 2σ level by chance
Sky map in equatorial coordinates of the 28 IceCube neutrinos (black circles) (IceCube Collaboration 2013) 36and Teles

events with E > 57 EeV and zenith angle ✓ < 55 (red small circles) (Abbasi et al. 2014). The TA hotspot is indicatedDiscussions- There is no speciﬁc high-E sources behind the hotspot.
- TA Hotspot is shifted from Supergalactic plane by 17 .
- Virgo cluster is really the brightest source in our FoV?

v Magnetic deﬂection- Galactic MF- Intergalactic MFv Mass Composition- TA measurement37

Galactic Magnetic Field

Generally regular MF

a few degrees for 1020 eV in the Galactic diskà too small? to explain hotspot shifted from SGPBut there are many MF models (Galactic disk + Halo).
Recent models suggest large & strong magnetic halo.
Jansson, R. & Farrar, G. R., ApJL, 761, L11 (2012)
Pshirkov, M., et al., ApJ, 738, 192 (2011)
Sun, X. H., et al., A&A, 477, 573 (2008)

38

!

Ed
≃ 0.52◦ q
θ(E, d) ≃rg
1020 eV"−1 !

d1 Mpc"!

B⊥
10−9 G".

(30)

Intergalactic Magnetic Field

Magnetic fields beyond the Galactic disk are poorly known and include a possible extended field in theGenerallyMF
halo of our Galaxy and a large scale EGMF. In both cases, the magnetic
field israndom
often characterized
by anr.m.s. strength B and a correlation length lc , i.e. it is assumed that its power spectrum has a cut-oﬀ inwavenumber space at k = 2π/lc and in real space it is-17
smooth on scales below-9 lc . If we neglect energy loss
processes for the moment, then the r.m.s. deflection angle over a distance d in such a field is

Very difficult to measure IGMF	

à Large uncertainty ~10 G < B < ~10 G	!

E(2dlc /9)1/2≃ 0.8◦ q
θ(E, d) ≃rg
1020 eV"−1 !

d10 Mpc"1/2 !

lc
1 Mpc"1/2 !

B
10−9 G",(31)for d >∼ lc , where the numerical prefactors were calculated from the analytical treatment in Ref. [260]. Thereit was also pointed out that there are two diﬀerent limits to distinguish: For dθ(E, d) ≪ lc , particles of allenergies “see” the same magnetic field realization during their propagation from a discrete source to theobserver. In this case, Eq. (31) gives the typical coherent deflection from the line-of-sight source direction,and the spread in arrival directions of particles of diﬀerent energies is much smaller. In contrast, fordθ(E, d) ≫ lc , the image of the source is washed out over a typical angular extent again given by Eq. (31),à too small? to explain
hotspot shifted from SGP

But, MF Strength depends oncluster / ﬁlament / void regions 28

A simulated universe
UHECR sources
Virtual observers
Ryu, Das & Kang, ApJ (2010)39

ysis using MD hybrid* events
Composition (Xmax)

refurbished TA
FD@MD]+ SD (Middle Drum Hybrid)
Measurement

log10(E/eV) > 19

<Xmax > [gm/cm2]

xiv:1408.1726)>10EeV : consistent with largely proton component
900

Data
QGSJETII−03
QGSJET−01c
SYBILL 2.1

850

800

Proton

750

Iron
700

2events

650>57EeV600

18.5

1919.5
20
Energy log (E/eV)
10

Abbasi, et Figureal, (arXiv:1408.1726)
28: The final Middle Drum hybrid composition
40
result using geometry and pattern recognition cuts forysis using MD hybrid* events
Composition (Xmax)

refurbished TA
FD@MD]+ SD (Middle Drum Hybrid)
Measurement

xiv:1408.1726)>10EeV : consistent with largely proton component

KS TestKS Test for QGSJET-II03
5%log10(E/eV) > 19

Lower energy side
Consistent with Proton

Abbasi, et al, (arXiv:1408.1726)

41

Summary• Current Results– We found evidence for the cosmic-ray hotspot
near the supergalactic plane, but shifted by ~17 .
– Chance probability assuming the isotropic sky isestimated to be 3.4σ for 5-year data.
à 4.0σ for 6-year data (New!)• Future Prospects– To reproduce the hotspot, we will start to ﬁnd
the best-estimate model assuming the GMF/IGMF,
the mass composition and the source distribution.
– We are now proposing the TAx4 project.
42TAx4 Proposal

TA High Energy Extension (TAx4)
Basically it uses same method as TA, with a FD and 3 times larger
coverage area by SDs. SD full area can not be covered by FD field ofview.

² Now there is hint of anisotropy
at >3σ level
northern issky.
This forexperiment
mainlyfor anisotropy study,v Plan to expand
4 timesThis is TAforby
detecting
2more cosmic (3,000kmrays which)
1. Add 500
scint.
counters
haveenergy
over GZK. Ifwithare
2.1 proton,km spacing
theytheir
2. 10 refurbished
HiRes
tels 50Mpc.
source iswithin
From our current result
the inconsistencyv Scienceof(3-yearobservation)withisotropy at high energy
region,1. Anisotropy
studywe are halfway toa clue?
à catching
Expect >>5σ	

2. Xmax & E Spectrumat the highest
energy construction.
regionNow, proposing
3. Search UHE photon & neutrino43