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C t yan

** **

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

For the Tibet AS Collaboration

Inst. for Cosmic Ray Research, Univ. of Tokyo

08 / 12 / 2006

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


The tibet as collaboration

The Tibet AS 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


Outline

Outline

  • The Tibet air-shower array

  • Anisotropy of galactic cosmic rays (*)

  • The tail-in and loss-cone model

  • Gamma/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 components

    • The ‘tail-in’ anisotropy component

    • Excesses from the Cygnus region(***)

  • Conclusive remarks


The tibet air shower array

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-scale

observation


Anisotropy of galactic cosmic rays

Anisotropy of galactic cosmic rays

4.0 TeV

6.2 TeV

12 TeV

50 TeV

300 TeV

i) Temporal variation

ii) Anisotropy towards the Cygnus region

iii) Energy dependency

iv) Anisotropy fade away ~ 300 TeV

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


Tail in and loss cone model of the anisotropy

loss-cone

tail-in

Galactic plane

Tail-in and loss-cone model of the anisotropy

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

< 1 TeV

  • Heliospheric magnetic field is not enough for TeV CR anisotropy.

  • TeV CR anisotropy should be caused by the Local Interstellar Could (~ a few pc).

RL~ 0.01pc (for 10TeV proton in 1mG)


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:

4.2 TeV, Gamma

8.1 TeV, Hadrons

Angular resolution

0.9o

The Gamma/Hadron Separation

  • Data sample here (1999 ~ 2004, 10 * 109)


Discrimination parameter for gamma and hadrons

R0 distributions & survival ratios

Discrimination parameter for gamma and hadrons

  • 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

Hadron (MC)

Gamma (MC)

Real Data

Syst ~= 5%

where Ri is the distance between ith fitted detector

and shower core in the shower-front plane.


Gamma hadron rejection and its quality factors

Quality factors:

Gamma/hadron rejection and its quality factors

  • 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

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


Back check by the crab nebula

Back-Check by the Crab Nebula

(The standard gamma-ray source)

Data analysis by azimuth swapping

~ 0.0046 +/- 0.00085

Before Cut

100% gamma-ray excess,

MC expected:0.0069 +/- 0.00012

(b)

Bin size: 1.7deg * 1.7 deg

~ 0.0077 +/- 0.0012

After Cut

(a)

~ 0.0031 +/- 0.00091

Comparison

(a)

(b)

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


Investigations on two anisotropy components the tail in and cygnus regions

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

Data analysis by weighted azimuth swapping

3.0 deg smoothed

Before Cut

After Cut

Comparison

100% CR excess assumption

100% gamma excess assumption


Hints on the tail in and the cygnus excesses

Hints on the Tail-in and the Cygnus excesses

Search Region (II)

Large-scale anisotropy removed

Gamma-like

Comparison

b = -5

100%

CRs Ex.

b = +5

b = +5

Comparison

100%

Gam. Ex.

b = -5

Search Region (I)

Hadron-like

Tail-In

Cygnus


C t yan

  • Investigation on the Tail-In anisotropy component:

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

“Tail-In”

Region

(Independent) bin size: 10 deg * 12 deg


C t yan

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

~ 0.0025 +/- 0.00014

Before Cut

If 100% gamma-ray,

reduced Excess to Background Ratio

~ 0.0025 +/- 0.00028

After Cut

= 0.0014 +/- 0.0008,

from the MC expectation.

Comparison

~ 0.0011 +/- 0.00015

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


C t yan

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

3.0 deg smoothed

Before Cut

After Cut

b = -5

Off2

On

Off1

b = +5

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

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


C t yan

Hadron Rejection:on & off the Galactic plane

off1

on

off2

Before Cut

~ 0.00065 +/- 0.00022

If 100% gamma,

MC expected:

0.00120 +/- 0.00045

After Cut

~ 0.00198 +/- 0.00045

Comparison

~ 0.00133 +/- 0.00040

Cygnus Region

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


Conclusive remarks

Conclusive 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.


Appendix background estimations

Appendix: background estimations

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

  • Technique of time swapping (from Milagro)

  • Azimuth swapping method

  • Weighted azimuth swapping method


Global cr intensity fitting method i

Global CR intensity fitting method (I)

Used in the published result

Reference:

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


Global cr intensity fitting method ii

Global CR intensity fitting method (II)

The background is estimated

by weighted azimuth swapping

A Technique of Data Shuffling

1) Auto event and background normalization

2) Auto azimuth correction in swapping M.C.


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