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Acceleration of ultra-high energy cosmic rays by cluster accretion shocks

Acceleration of ultra-high energy cosmic rays by cluster accretion shocks V.S. Ptuskin, S.I. Rogovaya, V.N. Zirakashvili IZMIRAN. HEA-2007. all-particle spectrum of cosmic rays at the Earth. modulation by solar wind. E -2.7. E -3. 1. GZK. energy losses of ultra-high energy cosmic rays

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Acceleration of ultra-high energy cosmic rays by cluster accretion shocks

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  1. Acceleration of ultra-high energy cosmic rays by cluster accretion shocks V.S. Ptuskin, S.I. Rogovaya, V.N. Zirakashvili IZMIRAN HEA-2007

  2. all-particle spectrum of cosmic rays at the Earth modulation by solar wind E-2.7 E-3.1 GZK

  3. energy losses of ultra-high energy cosmic rays in interstellar and intergalactic space Ec Ec,Fe microwave & FIR background energy loss time z = 0 • pair production pγ → pe+e- • pion production pγ → Nπ • GZK cutoff at Ec ~ 6×1019 eV expansion pairs pairs Greisen 1966; Zatsepin & Kuzmin 1966 • photodisintegration of nuclei • Ec,Fe ~ 2×1020 eV photodis- integration Stecker 1969 pions • Universe expansion - (1/E) (dE/dt)adiabatic = H H0=100h km/(s Mpc), h=0.71 Inoue et al. 2007

  4. rL= 10×E19/(Z×BμG) kpc mass composition limit of p/He acceleration in SNR ? Galactic extragalactic black body cutoff Galactic component:acceleration in SNRs with dispersion of SN & SNR parameters or early transitionto extragal. component + OB star associations, young pulsars, Galactic wind etc. extragalactic component: AGN & radiogalaxies, GRB, colliding galaxies, … , cluster accretion shocks Norman et al. 1995; Berezinsky et al. 1997; Kang et al. 1996, 1997, 2005; Ostrowski et al. 2002; Inoue et al. 2005, 2007; Gabici & Blasi 2005; Pierpaoli & Farrar 2005; Blasi et al. 2007

  5. cluster accretion shocks Keshet et al 2003 galaxy cluster ush Rsh ρ shock self-similar solution Bertschinger 1985 mass function Bahcall & Cen 1993 filaments

  6. diffusive shock acceleration Fermi 1949, Krymsky 1977, Bell 1978 … compression ratio ush ush/σ roughly Ncr ~ δ(E - Emax) Ncr ~ E-γ E < Emax δB acceleration efficiency ηcr = 2Fcr/(ρush3) σ + 2 γ= σ - 1 Pcr energy flux of run- away particles, ηcr<1 shock mhd turbulence in shock precursoris created selfconsi-stently by strongly driven Bell streaming instability of run- away protons Poster Zirakashvili & Ptuskin

  7. characteristics of particle acceleration by cluster accretion shocks cluster accretion 10 • energetics • 1040 erg/(s Mpc3) • at present epoch, z = 0 in cosmic rays 3×10-2 at < 1015 eV (SNR in normal galaxies); 2×10-3 at 1018-1020 eV SN 3×10-1 AGN 1 GRB 3×10-4 mechanical bolometric luminosity X/γ mechanical • observer is upstream of the shock: average source power density is a convolution of • ~ δ(E – Emax(Mcl)) with cluster mass function • acceleration against energy loss: Emax,Fe < 2×1020 eV at the source • assumed source composition: as in Galactic cosmic rays (where heavy element abundance is strongly enhanced) but suppressed by × 0.2 metal content (A>4)

  8. cosmic ray flux at the Earth after propagation through CMBR & FIRB ( ), preliminary ηcr = 0.7, no source evolution, data: -HiRes 2007, -Auger 2007 inferred Galactic component

  9. Conclusion Particle acceleration by cluster accretion shocks can be an efficient source of ultra high energy cosmic rays at 1018 to 1020 eV. It is characterized by favorable energetics, heavy nuclear composition at highest energies, and has a severe limit on particle energy at the sourceEmax,Fe< 2×1020 eV.

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