Towards unravelling the structural distribution of ultra-high-energy cosmic ray sources

Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008 1

Towards unravelling the structural distribution of ultra-high-energy cosmic ray sources

Hajime TakamiThe University of Tokyo

JSPS Fellow

Ref. HT and K. Sato, arXiv:0710.0767 HT and K. Sato,

arXiv:0711.2386

K. Sato (Univ. of Tokyo, IPMU), K. Murase, S.Nagataki (YICP), S.Inoue (NAOJ), T.Yamamoto (Konan Univ.)

Collaborators:


Cosmic-ray spectrum

Globally power-law spectrum Knee

SNRs for energetics Ankle (dip)

GCR/EGCR transition ? Pair creation dip ?

Extragalactic cosmic-rays Active Galactic Nuclei (AGNs) Gamma-ray bursts (GRBs) Magneters, colliding galaxie

s,.. Second Knee

Hypernovae (Gal/EG) ? GCR/EGCR transition ?

GZK steepening Composition Maximum acceleration energy

Flu

x [

m-2

sr-

1 s

-1 G

eV

-

1]

Energy [eV]

Knee

Second-Knee

Ankle (dip)

E-2.7

Galactic

EGG or EG ?

LHC max

Highly isotropic distribution


UHECR-AGN Positional Correlation

The collaboration pointed out that Extragalactic/Galactic magnetic fields are sufficiently weak Protons are dominated in highest energy cosmic-rays Spatial distribution of UHECR sources corresponds to that of nearby matter distr

ibution (especially supergalactic plane) 2 events around Cen A, the nearest radio loud AGN “hole” around Virgo cluster

Positional correlation between highest energy events and nearby extragalactic objects

( Pierre Auger Collaboration 2007)

Cen A

Supergalactic plane

Pierre Auger Observatory Argentina (35.2oS, 69.5oW) Mean altitude: 1400m Exposure: 9000km2 sr yr Angular resolution: less than 1o

Uncertainty in the energy scale: ~30%

E>57EeV, z<0.018 (75Mpc), =3.1o

Start charged particle astronomy


Charged particle (UHECR) astronomy

Statistical approaches --- large-scale and/or small-scale anisotropy Auto-correlation of events the number density of UHECR source

s (Blasi & De Marco 2004, Kacheliess & Semikoz 2005, HT & Sato 2006,2007) Cross-correlation What type of objects is UHECR source ? (Cuoco e

t al. 2007) Direct approaches --- small-scale anisotropy (AGASA collab.:Takeda et al. 1999)

Small-scale anisotropy the position of each UHECR source(HT & Sato 2007)

UHECR spectrum of each source(Blasi & De Marco 2004)

What is understood about the nature and origin of UHECRs from their arrival direction distribution ?

We have discussed the possibility of the charged particle astronomy before the Auger results using simulations taking into account UHECR source distribution and intervening magnetic fields which reflects the local universe actually observed.


Nearby universe ( d<100Mpc )

　　 If UHECR sources are astrophysical objects, UHECR arrival distribution should reflect nearby matter distribution and magnetic field distribution.

Nearby universe is not uniform

Perseus

Virgo

Centaurus

Hydra

A3627, Pavo

( IRAS PSCz Catalog: Saunders et al. 2000 )


Our models of UHECR source distribution and EGMF

Source distribution model Galaxies selected randomly from the modified IRAS catalog with several source

number densities. EGMF model

B ∝ m∝L

Magnetic field is normalized as 0.0, 0.1, 0.4G in the center of Virgo Cluster,

based on observations.

IRAS galaxies

Nearby matter distribution are constructed from IRAS PSCz catalog

Galaxies in the IRAS mask are assumed to be isotropic distribution.

( Takami et al. 2006 )(IRAS PSCz Catalog :d<100Mpc )

0 2 4

For B=0.1G

(100Mpc propagation of protons with 1020eV)


Calculation of the arrival distribution

1. Source distribution and extragalactic magnetic field are assumed. 2. UHECRs (protons) are propagated from the sources to the Earth takin

g energy-loss processes and the magnetic field into account. 3. UHECR arrival distribution can be simulated. 4. Comparing the simulated arrival distribution and the corresponding s

ource distribution, the positional correlation is investigated.

Investigate the positional correlation in simulation

This study has been performed before Auger result.

Energy-loss processesPhotopion production

Bethe-Heitler pair creation

Adiabatic energy-loss


GZK Mechanism (photopion production)

Cosmic-rays above 1020eV cannot be observed at the Earth

p

CMB

e

e+

++

e

e+

n p

Highest energy cosmic-rays can unveil nearby universe only within 100Mpc

E>6x1019eV

( Berezinsky 2007 )( HT+ 2007 )


An example of the arrival distribution (ns~10-

5Mpc-3)

Small-scale anisotropy

The arrival distribution predicted from the source distribution shown below.

Small-scale anisotropy is predicted in the directions of nearby sources

3000 events

even if EGMF is considered.


Another example of the arrival distribution (ns~10-

5Mpc-3)

The arrival distribution predicted from different source distribution from that last page, but the same source number density.

Predicted anisotropy is dependent on source distribution


Arrival distribution of UHE protons above 1019.8eV

200 event detection finds several strong event clusters The arrival distribution with 500 events traces nearby source

distribution as event clusters If ns is larger than 10-5Mpc-3, more event detection is required

for unveiling

10-5Mpc-

3Auger 5yr

of all the sky

A demonstration in the case of no EGMF

( HT & Sato 2007 )


Arrival distributions of UHE protons above 1019.8eV

Event clusters can be observed sufficiently although clustering signals become weak.

The positional correlation can be also observed.

Including EGMF

( HT & Sato 2007 )


Spatial Correlation : correlation value

1 : perfect correlation0 : no correlation

-1: perfect anti-correlation

Errors finite number of events

converges to some number of events, which is interpreted as the number to unveil the source distribution.

The number is dependent on the source number density.

10-4Mpc-3 :O(1000) events 10-5Mpc-3 :500 events

for E>1019.8eV

2ox2o

The correlation between UHECR arrival distribution and source distributions within

100Mpc.

( HT & Sato 2007 )


Spatial Correlation : correlation value

The converging values are different between source distribution with the same source number density.

But, the numbers of events that starts to converge are almost unchanged in 100 source distribution.

2ox2o

We calculate the averages and variances of the between 100 source distribution

( HT & Sato 2007 )


Models of Galacitc magnetic field Magnetic field in Galactic disk:

Bisymmetric(BSS) or Axisymmetric(ASS) BSS has field reversals, while ASS does not

Magnetic field in Galactic halo: much less known Spiral field with exponential decay in the z direction Classified by parity about Galactic plane ： symmetri

c(S) or anti-symmetric(A) A dipole field at Galactic center is also assumed

(Alvarez-Muniz & Stanev 2006)

Parity=A


Deflection angles of protons with 1019.8eV in GMF

The positional correlation is lost in the direction of the Galactic center due to strong deflections.

In the direction of the Galactic anti-center, the BSS models predicts smaller deflections than the ASS models. Thus, the northern observatories (such as Telescope Array) have an important role for correlation studies.

A blue region is toward Cen A.

What deflection angles do the arriving protons experience ?

( HT & Sato 2007 )


Deflection angles of protons with 1019.8eV in GMF

Several parameters in the GMF models are changed in the consistency with observations

The deflection angles can be 1-3o in the direction of the Galactic anti-center

UHECR Observatories in the terrestrial northern hemisphere are suitable for positional correlation studies !! Telescope Array


Summary

We have investigated the possibility of the charged particle astronomy before the Auger results using simulations including realistic models of UHECR source distribution and EGMF.

500 and O(1000) event detections above 1019.8eV can unveil the local distribution of UHECR sources for 10-5 and 10-4 Mpc-3, respectively even if EGMF is considered.

Galactic magnetic field contributes to the deflection of UHE protons to some extent.

Due to the GMF, UHECR observatories in the northern hemisphere are favored for positional correlation studies.

Documents

Towards unravelling the structural distribution of ultra-high-energy cosmic ray sources