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ultra high energy cosmic rays: theoretical aspects

ultra high energy cosmic rays: theoretical aspects. Daniel De Marco. Bartol Research Institute University of Delaware. plan. observations & open issues origin of UHECRs propagation: the GZK feature small scale anisotropies UHECRs,  -rays and s. direct observation.

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ultra high energy cosmic rays: theoretical aspects

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  1. ultra high energycosmic rays:theoretical aspects Daniel De Marco Bartol Research Institute University of Delaware

  2. plan observations & open issues origin of UHECRs propagation: the GZK feature small scale anisotropies UHECRs, -rays and s

  3. direct observation indirect observation (EAS) (1 particle per km2--century)

  4. direct observation indirect observation (EAS) (1 particle per km2--century) UHECR many joules inone particle

  5. spectrum AGASAHiResAuger arrival directions high energy AGASA composition arrival dirs. low energy Ostapchenko, Heck 2005 UHECRs: observations AGASA

  6. spectrum AGASAHiResAuger propagation production for astrophysical accelerators it is challenging to accelerate particles to such high energies. GZK feature in the energy spectrum due to the interactions with the photons of the CMB arrival directions high energy AGASA composition arrival dirs. low energy Ostapchenko, Heck 2005 UHECRs: observations two (separate) issues end of the CR spectrum at some high energy strong flux suppression around 5 x 1019eV AGASA

  7. origin of UHECRs bottom-up top-down • the energy flux embedded in a macroscopic motion or in magnetic fields is partly converted into energy of a few very high energy particles. • Shock acceleration at either Newtonian or Relativistic shocks. • Composition: nucleons (nuclei) • autolimiting: Emax ≤ Ze B L

  8. hillas plot Emax ≤ Ze B L Hillas 1984 accounting for energy losses the situation is even more difficult lines: 1020 eV Olinto 2000

  9. origin of UHECRs bottom-up top-down • the energy flux embedded in a macroscopic motion or in magnetic fields is partly converted into energy of a few very high energy particles. • Shock acceleration at either Newtonian or Relativistic shocks. • Composition: nucleons (nuclei) • autolimiting: Emax ≤ Ze B L • particle physics inspired models • UHECRs are generated by the decay of very massive particles mX» 1020 eV originating from high-energy processes in the early universe. • Topological Defects or SMRP • flatter spectra • Composition: dominated by photons • Constraints from the diffuse gamma rays flux measured by EGRET around 100 GeV

  10. propagation of UHECRs: protons • redshift losses • pair production (Eth ~ 5x1017 eV) pUHE +CMB N + e+ + e- • pion production (Eth ~ 7x1019 eV) pUHE +CMB N +  high inelasicity (20 – 50%) loss lengths GZK suppression: loss length @ 5x1019 eV = 1 Gpc loss length @ 1020 eV = 100 Mpc

  11. GZK feature: single source modification factor: observed spectrum / injection spectrum bump suppression

  12. similar conclusions for nuclei and gamma rays: CRs can not reach us at UHE if theyare generated at distances larger than about 100 Mpc(except neutrinos, violations of LI and so on) if the sources are uniformly distributed in the universe we should expect a suppression in the flux of UHECRs around 1020 eV

  13. AGASA & HiRes AGASA claims noGZK at 4 HiRes claims GZK at 4 a factor 2 in the flux HiRes: GZK AGASA: no GZK actual discrepanciesmore like~3 and ~2 DDM, Blasi, Olinto 2003, 2005

  14. systematic errors (?) AGASA -15%HiRes +15% agreement at low energy less disagreement at high energyhow much??~2 DDM, Blasi, Olinto 2003, 2005DDM, Stanev 2005

  15. some AGASA spectra DDM, Blasi, Olinto 2005

  16. both AGASA and HiRes do not have enough statistical power to determine if the GZK suppression is there or not

  17. auger:hybriddetection

  18. AGASAHiResAuger

  19. 1019eV Auger energy determination • reconstruct S(1000) • convert S(1000) to S38 using CIC curve • convert S38 to energy using the correlation determined with hybrid data

  20. Auger ICRC spectrum 444 17

  21. small scale anisotropy AGASA: 5 doublets + 1 triplet

  22. AGASA 2pcf point sources (?) DDM, Blasi, Olinto 2005 see also Finley and Westerhoff 2003

  23. B~<10-10 G resol.=2.5º =2.6 m=0E > 4x1019 eV - 57 events 10-6 Mpc-3 10-5 Mpc-3 10-4 Mpc-3 AGASA multiplets DDM, Blasi 2004

  24. sources characteristics LCR = 6x1044 erg/yr/Mpc3 (E>1019 eV - from spectrum fits) n0 = 10-5 Mpc-3(from ssa) Lsrc = 2x1042 erg/s (E>1019 eV) • are these ssa for real? • the significance of the AGASA result is not clear • HiRes doesn’t see them • some internal inconsistency

  25. AGASA spectrumdiscrete sources P: 6 10-4 2 10-4 : 3.2  3.7 DDM, Blasi, Olinto 2005

  26. arrival directions P~2 10-5 DDM, Blasi, Olinto 2005

  27. both the ssa and the spectrum measurement need more statistics to beconclusive and reliable

  28. galactic magnetic field regular + turbulent • spiral on the plane • exponential decay out of the plane (~1 kpc) • ~2 G at Sun position • Lmax ~ 100 - 500 pc • Bt ~ 0.5 - 2 Breg • spectrum: (??)kolmogorov, 5/3kraichnan, 3/2 sun RL(4x1019eV) = 20 kpc no big deflections except in the disk or in the center

  29. deflections in EGMF - 4x1019eV 110 Mpc Dolag at el. 2003: constrained simulation of the MF in the local universe MF in voids: 10-3-10-1nGMF in filaments: 0.1-1 nG • deflections • >1o in less than 2% of sky • self-similarity>1o in less than 30% of sky up to 500 Mpc CR astronomy (maybe) possible Sigl et al. 2004: very similar approach, completely different results. Fields in voids higher by 2-4 orders of magnitude. CR astronomy definitely impossible

  30. UHECRs, neutrinos and gamma rays interaction of accelerated protons in the sources or during propagation • the neutrino spectrum is unmodified, except for redshift losses • gamma rays pile up below the pp threshold on the CMB (~ few 1014eV)universe = calorimeter EGRET diffuse gamma ray flux(MeV - 100 GeV) produces a constraint on neutrino fluxes Lee 1998

  31. from EG GR bg max.EG pflux p/ horizon ratio (thin) EG p: E-2 Mannheim, Protheroe, Rachen 2000 CR bound on  from astrophysical sources Waxman & Bahcall 1998 1019 - 1021eV EGCR spectrum: energy density of muon neutrinos fraction of energy lost fraction going in neutrinos not valid for top-down sources,optically thick sources…

  32. W&B from neutron decay from neutronspion-production Engel, Seckel, Stanev 2001 GZK neutrinos rates per km3 water per year: 0.1-0.2

  33. issues/questions for the future • increase statistics above 1020eV: is the GZK feature present? (solve SD-FD discrepancy) • increase statistics above 4x1019 eV to identify ssa and possibly determine density of sources • measure chemical composition at low energy to determine where the G-XG transition is occurring and at high energy to understand the nature of UHECRs • multifrequency observation of the sources

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