Propagation of UHE protons in magnetized large scale structure

1. Propagation of UHE protons in magnetized large scale structure Santabrata Das ARCSEC, Sejong University, South Korea. • Collaborators: • Heysung Kang, PNU, Korea. • Dongsu. Ryu, CNU, Korea. • Jungyeon. Cho, CNU, Korea.

2. Introduction • Earth’s atmosphere is continuously bombarded by extremely high energetic particles. • Such particles strikes every 100 sq.km/yr and form the tail of the cosmic-ray spectrum that extends from 1Gev to beyond 100EeV. • We know little about them, in particular, we do not understand clearly how and where these particles gain their remarkable energies. • They may be the evidence of unknown physics or of exotic particles formed in the early universe. • They are possibly the only samples of extragalactic materials that can be detect directly.

3. Observed energy spectrum of Cosmic Rays Nagano, M. and Watson, A. A., 2000, Rev. Mod. Phys., 72, 689

4. Enigma of UHECRs Gyroradius: • A cutoff in spectrum around 50 EeV is expected due to the interaction of particles with CMB photons (GZK limit). • Observations establish particles with E > 50EeV. • This follows a nearby sources on cosmological scale. • No nearby astronomical source have yet been identified.

5. Composition of UHECRs • Experimental studies of extended air shower establish the fact in favour of light composition above 10 EeV (Abbasi et al. 2005). This are in very good agreement with the HiRes, Yakutsk, Haverah Park data (Ave, M., et al, Astropart. Phys., 2003, 19, 47; Abu-Zaayad, T., et al, PRL., 2005, 84. 4276; Glushkov, A. V., et al, JETP Lett., 2000, 71, 97). • UHECR composition is dominated by proton, although a mixed composition dominated by heavier nuclei cannot be ruled out.

6. Origin of UHECRs • UHECR sources need to satisfy few conditions: • Source must be strongly luminous and powerful. • It must accelerate particles above E_max > 1000 EeV. Astrophysical Sources : • Active Galactic Nuclei • Gamma Ray Bursts • Cosmological Shocks • Etc.

7. Extragalactic magnetic fields • The strength and morphology of the intergalactic magnetic fields remain largely unknown as it is intrinsically difficult to observe. So far, direct evidence for the presence of the EGMFs has been found only in galaxy clusters. • Geometry of cosmic magnetic field (special distribution of field strength and its orientation) is strongly correlated with large scale non-linear structures of the universe. This suggests, the field strength increases with the matter density.

8. Numerical Simulation of large scale structure of the universe Lcold dark matter cosmology L = 0.73, DM = 0.27, gas = 0.043, h=0.7, n = 1, 8 = 0.8 Computational box: (100 h-1 Mpc)3 : grid-based Eulerian TVD code. (Ryu, Kang et al 2003, 2005) 6 sets of different realizations of initial conditions are used. EGMF model: (Bx, By, Bz) are obtained from 1. Passively evolving B fields in the simulations  directional information 2. Vorticity of flows  magnitude of B fields (based on turbulent dynamo)

9. Turbulent Dynamo model • Magnetic field is assumed to result from the turbulent motion of the intergalactic gas. • EGMFs are computed directly by equating magnetic energy to the suitable fraction of turbulent energy of intergalactic gas.

10. Magnetic field strength in large scale structure of the universe Clusters Filaments Sheets Voids • inside clusters, B ~ a few mG • around clusters (T > 107 K), B ~ 0.1 mG • in filaments (105 K < T < 107 K), B ~ 10 nG • in sheets (104 K < T < 105 K), B ~ 10-10 G • in voids (T < 104 K), B ~ 10-12 G

11. 2-D cuts of baryonic density & EGMFs

12. CR sources and observers • CR Sources : • AGNs inside galaxy cluster with kT > 1.0 keV. • 20-30 sources in the simulated volume with source density • Mean separation • Most massive cluster with

13. ` CR sources and Observers • Observer locations: • Groups of galaxies with 0.05keV < kT < 0.5 keV. • 1000 – 1300 observers in the simulated volume. • Groups along filaments with

14. Source-Observer locations inside Simulation Volume

15. CR injection & propagation through magnetized universe • CR injection: • for • 30000 protons launched into random direction from “sources”. • CR propagation: • Solve the equation of motion. • B field: our turbulent dynamo model. Energy losses : • Pair-production : • Pion production : 100EeV proton loses 1/e of its energy in ~140 Mpc

16. CR Injection & propagation through magnetized universe • CR observation: • Passage within the “observer sphere” with • Arrival direction (q): deflection angle from “source” position. • Time delay : relative to the rectilinear propagation. • Continue its journey until proton loses energy down to 10EeV. • Multiple visits ~ observed events.

17. Particle trajectories in EGMFs • Random injection. • 100h^{-1}Mpc spatial distance propagation. • Energy loss considered.

18. Particle trajectories in EGMFs • Random injection. • 100h^{-1}Mpc spatial distance propagation. • Energy loss considered.

19. Particle trajectories in EGMFs • Random injection. • 100h^{-1}Mpc spatial distance propagation. • Energy loss considered.

20. Particle trajectories in EGMFs • Random injection. • 100h^{-1}Mpc spatial distance propagation. • Energy loss considered.

21. Distribution of deflection angles g = 2.7 E > 50 EeV Kang, et al., ICRC, 2007

22. Distribution of UHECR detection energy E and deflection angle g = 2.7

23. Distribution of time delay g = 2.7 E > 10 EeV E > 100 EeV Kang, et al., ICRC, 2007

24. Distribution of UHECR detection energy E and Time delay g = 2.7

25. Energy spectrum of observed protons Log E (eV) Kang, et al., ICRC, 2007

26. Summary: • Below GZK energy, the deflection angles and time delay are substantial. • Around 20 % of super-GZK events are expected to arrive at Earth within TWO degree. • UHE charged particle astronomy may be possible for E > 100 EeV. • Predicted UHE proton spectrum with g = 2.4-2.7 fits HiRes data and exhibits the GZK cutoff.

27. Thank you