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

Towards unravelling the structural distribution of ultra-high-energy cosmic ray sources. Hajime Takami The University of Tokyo JSPS Fellow. Collaborators:. K. Sato (Univ. of Tokyo, IPMU), K. Murase, S.Nagataki (YICP), S.Inoue (NAOJ), T.Yamamoto (Konan Univ.).

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

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  1. Towards unravelling the structural distribution of ultra-high-energy cosmic ray sources Hajime Takami The University of Tokyo JSPS Fellow Collaborators: K. Sato (Univ. of Tokyo, IPMU), K. Murase, S.Nagataki (YICP), S.Inoue (NAOJ), T.Yamamoto (Konan Univ.) Ref. HT and K. Sato, arXiv:0710.0767 HT and K. Sato, arXiv:0711.2386 Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  2. 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 galaxies,.. • Second Knee • Hypernovae (Gal/EG) ? • GCR/EGCR transition ? • GZK steepening • Composition • Maximum acceleration energy E-2.7 Knee Flux [m-2 sr-1 s-1 GeV-1] Highly isotropic distribution LHC max Galactic Second-Knee G or EG ? EG Ankle (dip) Energy [eV] Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  3. 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 distribution (especially supergalactic plane) 2 events around Cen A, the nearest radio loud AGN “hole” around Virgo cluster 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% UHECR-AGN Positional Correlation Positional correlation between highest energy events and nearby extragalactic objects Cen A Start charged particle astronomy E>57EeV, z<0.018 (75Mpc), d=3.1o Supergalactic plane ( Pierre Auger Collaboration 2007) Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  4. Charged particle (UHECR) astronomy What is understood about the nature and origin of UHECRs from their arrival direction distribution ? • Statistical approaches --- large-scale and/or small-scale anisotropy • Auto-correlation of events  the number density of UHECR sources (Blasi & De Marco 2004, Kacheliess & Semikoz 2005, HT & Sato 2006,2007) • Cross-correlation  What type of objects is UHECR source ? (Cuoco et 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) 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. Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  5. If UHECR sources are astrophysical objects, UHECR arrival distribution should reflect nearby matter distribution and magnetic field distribution. Nearby universe ( d<100Mpc ) Nearby universe is not uniform Virgo Centaurus Hydra A3627, Pavo Perseus ( IRAS PSCz Catalog: Saunders et al. 2000 ) Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  6. Source distribution model Galaxies selected randomly from the modified IRAS catalog with several source number densities. EGMF model B ∝ rm2/3 ∝ rL2/3 Magnetic field is normalized as 0.0, 0.1, 0.4mG in the center of Virgo Cluster, based on observations. Our models of UHECR source distribution and EGMF Nearby matter distribution are constructed from IRAS PSCz catalog IRAS galaxies (100Mpc propagation of protons with 1020eV) 0 2 4 For B=0.1mG (IRAS PSCz Catalog :d<100Mpc ) ( Takami et al. 2006 ) Galaxies in the IRAS mask are assumed to be isotropic distribution. Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  7. Source distribution and extragalactic magnetic field are assumed. UHECRs (protons) are propagated from the sources to the Earth taking energy-loss processes and the magnetic field into account. UHECR arrival distribution can be simulated. Comparing the simulated arrival distribution and the corresponding source distribution, the positional correlation is investigated. Calculation of the arrival distribution Investigate the positional correlation in simulation Energy-loss processes Photopion production Bethe-Heitler pair creation Adiabatic energy-loss This study has been performed before Auger result. Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  8. GZK Mechanism (photopion production) Cosmic-rays above 1020eV cannot be observed at the Earth e+ CMB g m+ E>6x1019eV nm p+ ne nm p e+ n p ne ( HT+ 2007 ) ( Berezinsky 2007 ) Highest energy cosmic-rays can unveil nearby universe only within 100Mpc Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  9. An example of the arrival distribution (ns~10-5Mpc-3) The arrival distribution predicted from the source distribution shown below. Small-scale anisotropy 3000 events Small-scale anisotropy is predicted in the directions of nearby sources even if EGMF is considered. Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

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

  11. 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 Arrival distribution of UHE protons above 1019.8eV A demonstration in the case of no EGMF 10-5Mpc-3 Auger 5yr of all the sky ( HT & Sato 2007 ) Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  12. Event clusters can be observed sufficiently although clustering signals become weak. The positional correlation can be also observed. Arrival distributions of UHE protons above 1019.8eV Including EGMF ( HT & Sato 2007 ) Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  13. Errors finite number of events X 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 Spatial Correlation : correlation value X The correlation between UHECR arrival distribution and source distributions within 100Mpc. 2ox2o 1 : perfect correlation 0 : no correlation X = -1: perfect anti-correlation ( HT & Sato 2007 ) Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  14. The converging values are different between source distribution with the same source number density. But, the numbers of events that X starts to converge are almost unchanged in 100 source distribution. Spatial Correlation : correlation value X We calculate the averages and variances of the X between 100 source distribution 2ox2o ( HT & Sato 2007 ) Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

  15. 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：symmetric(S) or anti-symmetric(A) A dipole field at Galactic center is also assumed Models of Galacitc magnetic field Parity=A (Alvarez-Muniz & Stanev 2006) Accelerators in the Universe @ KEK, Tsukuba Mar. 14, 2008

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

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

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

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