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Multi-TeV Observation on the Galactic Cosmic Ray Anisotropy in the Tail-In and Cygnus Regions

by the Tibet-III Air Shower Array

C. T. Yan

08 / 12 / 2006

Inst. for Cosmic Ray Research, Univ. of Tokyo

” Locating PeV Cosmic-Ray Accelerators: Future Detectors in Multi-TeV Gamma-Ray Astronomy ” 6 – 8 December, 2006 - Adelaide, Australia

For the Tibet AS Collaboration

** **

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The Tibet ASThe Tibet AS Collaboration Collaboration

M.Amenomori,1 S.Ayabe,2 X.J.Bi,3 D.Chen,4 S.W.Cui,5 Danzengluobu,6 L.K.Ding,3 X.H.Ding, 6

C.F.Feng,7 Zhaoyang Feng,3 Z.Y.Feng,8 X.Y.Gao,9 Q.X.Geng,9 H.W.Guo,6 H.H.He,3 M.He,7 K.Hibino,10

N.Hotta,11 HaibingHu,6 H.B.Hu,3 J.Huang,12 Q.Huang,8 H.Y.Jia,8 F.Kajino,13 K.Kasahara,14Y.Katayose,4

C.Kato,15 K.Kawata,12 Labaciren,6 G.M.Le,16 A.F. Li,7 J.Y.Li,7 Y.-Q. Lou,17 H.Lu,3 S.L.Lu,3 X.R.Meng,6

K.Mizutani,2,18 J.Mu,9 K.Munakata,15 A.Nagai,19 H.Nanjo,1 M.Nishizawa,20 M.Ohnishi,12 I.Ohta,21 H.Onuma,2

T.Ouchi,10 S.Ozawa,12 J.R.Ren,3 T.Saito,22 T.Y.Saito,23 M.Sakata,13 T.K.Sako,12 T.Sasaki,10 M.Shibata,4

A.Shiomi,12 T.Shirai,10 H.Sugimoto,24 M.Takita,12 Y.H.Tan,3 N.Tateyama,10 S.Torii,18 H.Tsuchiya,25

S.Udo,12 B. Wang,9 H.Wang,3 X.Wang,12 Y.G.Wang,7 H.R.Wu,3 L.Xue,7 Y.Yamamoto,13 C.T.Yan,12

X.C.Yang,9 S.Yasue,26 Z.H.Ye,16 G.C.Yu,8 A.F.Yuan,6 T.Yuda,10 H.M.Zhang,3 J.L.Zhang,3 N.J.Zhang,7

X.Y.Zhang,7 Y.Zhang,3 Yi Zhang,3 Zhaxisangzhu,6 and X.X.Zhou 8

(1) Dep. of Phys., Hirosaki Univ., Hirosaki, Japan(2) Dep. of Phys., Saitama Univ., Saitama, Japan(3) Key Lab. of Particle Astrophys., IHEP, CAS, Beijing, China(4) Fac. of Eng., Yokohama National Univ., Yokohama , Japan(5) Dep. of Phys., Hebei Normal Univ., Shijiazhuang, China(6) Dep. of Math. and Phys., Tibet Univ., Lhasa, China(7) Dep. of Phys., Shandong Univ., Jinan, China(8) Inst. of Modern Phys., South West Jiaotong Univ., Chengdu, China(9) Dep. of Phys., Yunnan Univ., Kunming, China(10) Fac. of Eng., Kanagawa Univ, Yokohama, Japan(11) Fac. f of Educ., Utsunomiya Univ., Utsunomiya, Japan(12) ICRR., Univ. of Tokyo, Kashiwa, Japan(13) Dep of Phys., Konan Univ., Kobe, Japan(14) Fac. of Systems Eng., Shibaura Inst. of Tech., Saitama, Japan

(15) Dep. of Phys., Shinshu Univ., Matsumoto, Japan(16) Center of Space Sci. and Application Research, CAS, Beijing, China(17) Phys. Dep. and Tsinghua Center for Astrophys., Tsinghua Univ., Beijing, China (18) Advanced Research Inst. for Sci. and Engin., Waseda Univ., Tokyo, Japan(19) Advanced Media Network Center, Utsunomiya University, Utsunomiya, Japan(20) National Inst. of Info., Tokyo, Japan(21) Tochigi Study Center, Univ. of the Air, Utsunomiya, Japan(22) Tokyo Metropolitan College of Industrial Tech., Tokyo, Japan(23) Max-Planck-Institut fuer Physik, Muenchen, Germany (24) Shonan Inst. of Tech., Fujisawa, Japan(25) RIKEN, Wako, Japan(26) School of General Educ.,Shinshu Univ., Matsumoto, Japan

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OutlineOutline • The Tibet air-shower array

• Anisotropy of galactic cosmic rays (*)Anisotropy of galactic cosmic rays (*)• The tail-in and loss-cone model

• Gamma/hadron separation methodGamma/hadron separation method– Discrimination of gamma/hadron in the array– Gamma/Hadrons judgment by comparisons (**)

• Back-check by the Crab Nebula

• Investigation on two anisotropy componentsInvestigation on two anisotropy components– The ‘tail-in’ anisotropy component– Excesses from the Cygnus region (***)

• Conclusive remarks

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The Tibet air shower array

View around the Tibet III array (90.52E, 30.10N;4300m a.s.l.) in 2003

– Located at an elevation of 4300 m (Yangbajing in Tibet, China)

– Atmospheric depth 606 g / cm2

– Wide field of view ( ~ 2 sr field of view)– High duty cycle ( > 90%)– Modal energy: ~ 3 TeV– Angular resolution: ~ 0.9o – Data sample used (1997 ~ 2005, 37 * 109)

Large-scaleLarge-scaleobservationobservation

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Anisotropy of galactic cosmic rays

4.0 TeV

6.2 TeV

12 TeV

50 TeV

300 TeV

From Science, V314, pp.439 – 443 (2006), by the analysis method (I)

i) Temporal variation

ii) Anisotropy towards the Cygnus regionAnisotropy towards the Cygnus region

iii) Energy dependency

iv) Anisotropy fade away ~ 300 TeV

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loss-cone

tail-inGalactic plane

Tail-in and loss-cone model of the anisotropyTail-in and loss-cone model of the anisotropy

1) Heliospheric magnetic field is not enough for TeV CR anisotropy.2) TeV CR anisotropy should be caused by the Local Interstellar Could (~ a few pc).

RRLL~ ~ 0.01pc0.01pc (for 10TeV proton in 1mG) (for 10TeV proton in 1mG)

Ref: K. Nagashima, K. Fujimoto, R.M. Jacklyn, J. Geophys. Res. V103, 17429 (1998).

< 1 TeV< 1 TeV

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The Gamma/Hadron Separation

• Gamma-initiated air shower – Concentrated– Smooth– Uniformity– …

• Hadron-initiated air shower– Scattered– Large fluctuation– Sub core structure– …

• Simulations:– Corsika-6.204 for air showers– Epicsuv-8.00 for array detectors– Energy: 300 GeV – 10 PeV– E-2.7, Hadrons (comp. HD4)– E-2.6, Gamma (Crab-like)

• Data cuts:– Zenith < 45o

– Core inside array– Residual error < 1.0 m– 1.25 p / any 4– 30.0 < Sum_pFT <= 100.0

• Representative energy:Representative energy:– 4.2 TeV, Gamma– 8.1 TeV, Hadrons

• Angular resolutionAngular resolution– 0.9o

Data sample here (1999 ~ 2004, 10 * 10Data sample here (1999 ~ 2004, 10 * 1099))

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Discrimination parameter for gamma and hadrons

• R0 distributions & survival ratios • Separation parameter– Global parameter

• Mean distance to core

• Virial distance of shower

• Hit_max to core

• Out core / All

– Cluster parameter• Num_clus / Num_hit

• Lateral distance of clus

• Steepness of clus

• Out_pixel / all_pixel

– Image (FFT) parameter • 1st freq / DC

• 2nd freq / DC

• 1st freq / All

• 2nd freq / All

where Ri is the distance between ith fitted detector

and shower core in the shower-front plane.

Gamma (MC)Gamma (MC)

Hadron (MC)Hadron (MC)

Real Data

Syst ~= 5%

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• Rejection method

– Excess to Bkgrd Ratio (E2BR):

• E/B: E2BR before cut• E’/B’: E2BR after cut• Gamma survival ratio• Hadron survival ratio

– Expectation:• 100% gamma: E = E’• 100% hadron: E = E’’• Where E’’ = ** E’

– Hypothesis Rejection:• 100% gamma by• Quality factor1• 100% hadron by• Quality factor2

Gamma/hadron rejection and its quality factors

• Quality factors:

The key point is to compare the data sample before cut and after cut !!The key point is to compare the data sample before cut and after cut !!

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~ 0.0046 +/- 0.00085~ 0.0046 +/- 0.00085

~ 0.0077 +/- 0.0012~ 0.0077 +/- 0.0012

~ 0.0031 +/- 0.00091~ 0.0031 +/- 0.00091

MC expected: 0.0069 +/- 0.00012

100% gamma-ray excess,

Hadron (100%) is rejected at 3.4 sigma; Data is consistent with gamma(100%) at 0.8 sigma.

Back-Check by the Crab NebulaData analysis by azimuth swapping(The standard gamma-ray source)(The standard gamma-ray source)

Before CutBefore Cut

After CutAfter Cut

ComparisonComparison

(b)

(a)

(a) (b)

Bin size: 1.7deg * 1.7 deg

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Investigations on Two Anisotropy Components: the Tail-In and Cygnus regions

3.0 3.0 deg smootheddeg smoothed

Before CutBefore Cut

After CutAfter Cut

ComparisonComparison

100% CR excess assumption 100% gamma excess assumption

Data analysis by weighted azimuth swapping

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Hints on the Tail-in and the Cygnus excessesHints on the Tail-in and the Cygnus excesses

Gamma-like

Hadron-like

Large-scale anisotropy removed

b = -5

b = +5

b = -5

b = +5

Search Region (II)Search Region (II)

Search Region (I)Search Region (I)

ComparisonComparison

ComparisonComparison

100%CRs Ex.

100%Gam. Ex.

Tail-InTail-In CygnusCygnus

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• Investigation on the Tail-In anisotropy component:Investigation on the Tail-In anisotropy component:

Use it as the background source ( Is it CR !?Is it CR !? )

(Independent) bin size: 10 deg * 12 deg

““Tail-In”Tail-In” RegionRegion

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~ 0.0025 +/- 0.00014~ 0.0025 +/- 0.00014

~ 0.0025 +/- 0.00028~ 0.0025 +/- 0.00028

~ 0.0011 +/- 0.00015~ 0.0011 +/- 0.00015

Gamma (100%) is rejected at 7.4 sigma; Data is consistent with hadron (100%) at 0.1 sigma.

If 100% gamma-ray,

from the MC expectation.

reduced Excess to Background Ratio

= 0.0014 +/- 0.0008,

Before CutBefore Cut

After CutAfter Cut

ComparisonComparison

( Is it CR !?Is it CR !? The GeV underground muon Exp. gives the answer is Yes !)

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• Investigation on the excess from the Cygnus regionInvestigation on the excess from the Cygnus region (gamma point source, diffuse gamma-ray emissions)

After g/p cut, Excess to Background Ratio will be enhanced, if excess is from gamma. See next After g/p cut, Excess to Background Ratio will be enhanced, if excess is from gamma. See next

( Cross + is MGRO J2019+37 MGRO J2019+37) +/- 3.0 deg

Before CutBefore Cut

After CutAfter CutOnOn

Off1Off2

b = +5

b = -5

3.0 3.0 deg smootheddeg smoothed

16Hadron (100%) is rejected at 3.4 sigma; Data is consistent with gamma (100%) at 1.8 sigma.

Hadron Rejection:Hadron Rejection: onon & & offoff the Galactic plane

onon

Cygnus Region

~ 0.00065 +/- 0.00022~ 0.00065 +/- 0.00022

~ 0.00198 +/- 0.00045~ 0.00198 +/- 0.00045

~ 0.00133 +/- 0.00040~ 0.00133 +/- 0.00040

MC expected:0.00120 +/- 0.00045

If 100% gamma,

off1off1 off2off2

ComparisonComparison

After CutAfter Cut

Before CutBefore Cut

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Conclusive RemarksConclusive Remarks

• The Crab excess is consistent with 100% gamma assumption at 0.8 sigma level, and 100% CRs assumption is rejected at 3.4 sigma level. (The CRs rejection is MC-independent).

• The Tail-In region anisotropy is from CRs except the small region including the Crab Nebula. 100% gamma excess assumption is rejected at 7.4 (3.5 [large-scale anisotropy removed]) sigma level. And 100% CR excess assumption is consistent at 0.1 (0.4 [large-scale anisotropy removed]) sigma level.

• As the original excess from the Cygnus region in our search window (-4.0o < b < 2.0o, 72.0o < l < 78.0o) is at 3.3 sigma level, we cannot effectively judge it is from gamma-ray or CRs. CRs rejection is at about 3.4 sigma level. And the gamma-ray consistence is at about 1.8 sigma level. Due to the fluctuations, here the result shows the excess is over gamma-like. But the (diffuse) gamma-ray emission hypothesis is slightly favored.

• Further improvement using multi-parameters is in progress.

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Appendix: background estimationsAppendix: background estimations

• Global CR intensity fitting methods (I), (II)

• Technique of time swapping (from Milagro)

• Azimuth swapping method

• Weighted azimuth swapping method

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Z e n i t h

O n - s o u r c e

O f f - s o u r c eO f f - s o u r c e

,o n o nI N o n

o n

I

N

o f f

o f f

I

N

2

o n o n o f f , i o f f , ii i2

t , o n 2

2 2o n o n o f f , i o f f , i

i i

N I - N I 1

χ =

N I + N I 1

2 2,

,t o t a l i t o n

t o n

I

E q u a l

,o f f o f fI N

Global CR intensity fitting method (I)

Reference: M. Amenomori, et al., ApJ. V633, 1005 (2005)

Used in the published resultUsed in the published result

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Global CR intensity fitting method (II)

onon

b

NI

N

The background is estimated by weighted azimuth swapping

A Technique of Data Shuffling

1) Auto event and background normalizationAuto event and background normalization

2) Auto azimuth correction in swapping M.C.Auto azimuth correction in swapping M.C.