Extragalactic sources and Extragalactic sources and ultra- -high energy cosmic rays high energy cosmic rays ultra Athina Meli (Peter Biermann, John Quenby, Julia Tjus, Paolo Ciarcelluti) Faculty of Sciences Department of Physics and Astronomy University of Ghent Belgium Seminar Goethe University Frankfurt am Main 09 June 2015 Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Outline � Cosmic-ray spectrum characteristics � Sources (non- & relativistic) � Shocks and jets - Properties - Particle acceleration mechanism � Shock acceleration simulation studies overview - Numerical method - Individual and multiple relativistic shocks in AGN - Propagation and radiation � Conclusion Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Cosmic-rays � Cosmic-rays are subatomic particles & radiation of extra-terrestrial origin. � First discovered in 1912 by Victor Hess , measuring radiation levels aboard a balloon up to 5300m � Hess found increased radiation levels at higher altitudes: named it Cosmic Radiation Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Cosmic-ray spectrum ~E -2.7 ~E -3 knee 1 part m -2 yr -1 Auger TA ~E -2.7 Ankle 1 part km -2 yr -1 LHC Toe 1 part km -2 cent -1 [T. Gaisser 2005] Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
The high energy regime - ‘knee(s)’ & ‘ankle’ Non-relativistic sources SN/X-ray binaries/pulsars -galactic- 2 nd knee R e l a t i v - i e s x t 1 st knee i t c r a AGN/GRBs s g o a u l a r c c e t i s c - Or run-out of fuel ? toe ankle GZK cut-off ? Greizen, Zatsepin & Kumzin (1966) Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
The ultra-high energy regime – the ‘toe’ …EUSO in orbit EUSO in orbit… Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Cosmic-ray sources and Hillas criterion maximum energies � Magnetic field dimensions sufficient to contain the accelerating particles � Strong fields and large plasma speeds ≈ β ≈ β ≈ β ≈ β ⋅ ⋅ ⋅ ⋅ µ µ µ µ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ 18 E Z B[ G] L[kpc] 10 eV max shock ISM-SN: (Lagage & Cesarsky, 1983) Hillas (1984) Wind-SN: (Biermann, 1993) AGN radio-lobes: (Rachen & Biermann,1993) AGN Jets or cocoon: (Norman et al.,1995) AGN multiple-shock-jet: (Meli & Biermann, 2013) GRB: (Meszaros & Rees, 1992,1994) Neutron stars: (Bednarek & Protheroe, 2002) Pulsar wind shock: (Berezhko, 1994) Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Sources: Non-relativistic Relativistic Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Sources: Non-relativistic Relativistic Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Supernovae L ~ 10 41-43 erg/s L ~ 10 41-43 erg/s Γ Γ Γ Γ ~ 1-2 Γ ~ 1-2 Γ Γ Γ E max ~ 10 16 eV � � � � 10 17.5 eV E max ~ 10 16 eV � � 10 17.5 eV � � e.g. Berezinsky & Ginzburg ’87, e.g. Berezinsky & Ginzburg ’87, (e.g. Meli & Biermann ’ 06) (e.g. Meli & Biermann ’ 06) Giacobbe ’05, Giacobbe ’05, Aharonian et al. (HESS) ‘06 Aharonian et al. (HESS) ‘06 Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
SN 1987A Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Sources: Non-relativistic Relativistic Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Active Galactic Nuclei Jets L ~ 10 46 erg/s L ~ 10 46 erg/s Γ Γ Γ Γ ~ 10-30 Γ Γ ~ 10-30 Γ Γ E max ~ 10 19-21 eV E max ~ 10 19-21 eV e.g. Meier ’03, e.g. Meier ’03, Georganopoulos ’05, Georganopoulos ’05, Marcher et al. ’08, ‘12 Marcher et al. ’08, ‘12 Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Gamma Ray Bursts Jets L ~ 10 51 erg/s L ~ 10 51 erg/s 100 < Γ Γ Γ Γ <1000 100 < Γ Γ Γ Γ <1000 E max ~ 10 21 eV E max ~ 10 21 eV e.g. Cavallo & Rees ‘78, Goodman ‘86, Paczynski ’86, e.g. Cavallo & Rees ‘78, Goodman ‘86, Paczynski ’86, Vietri ’95, Waxmann ’00, etc Vietri ’95, Waxmann ’00, etc Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
A ‘hidden force’ in extragalactic jets: Shocks Shocks Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Individual or multiple shocks Supersonic/superalfvenic strong compression waves � � � � change gas/plasma’s v, d, p, T - Collisional shocks (ordinary fluid) - Colissionless astrophysical shocks: In diffuse regions, low densities, large bulk speeds PKS 1510-089 PKS 0637-752 M87 CenA Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Shock classification - magnetic field orientation l a n i m u l r e p u S -z y l a n i m u ) e l u b q u i S l b o ( Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Shock jump-conditions (Rankine-Hugoniot relations) � � � � V 1 V 2 � � MHD � � Rankine (1870), Hugoniot (1887) Parker (1965), Hudson (1965), Parks (1984) Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Particle acceleration mechanism at shocks No doubt collisionless astrophysical shocks accelerate particles Convincing evidence (early 80s) for efficient acceleration in heliospheric shocks and in SNRs Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
The Fermi mechanism Transfer of the macroscopic kinetic energy of moving magnetized plasma to individual charged particles � � � � non-thermal distribution � 2nd order Fermi acceleration (Fermi ‘49,’54) @magnetic plasma clouds � 1st order Fermi acceleration - diffusive acceleration (Krymskii ‘77, Bell ‘78, Blandford & Ostriker ‘78, Axford et al. ‘78) @plasma shocks Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
1st order Fermi acceleration – diffusive acceleration of CRs � Test particle - diffusion - n acceleration shock cycles ( ) 1 n = + ⋅ E x E 0 n � Probability of scattering x av.no. scatterings x ∆ ∆ ∆ ∆ E Energy gain: fraction of initial energy ∆ = − = ⋅ E E E x E 0 0 Upstream Downstream � Average energy gain per collision: < ∆ / >≅ ( 2 / ) E E V c � Leading to a power-law energy behaviour ∞ ( ) ∑ ( ) ( ) 1 n E ... − σ > = − = ∝ N E P E esc i = n σ = (r+2)/(r-1), r = V 1 /V 2 = ( γ +1) / ( γ -1) for mono-atomic gas: γ =5/3 � r = 4 � E -2 Important: Non-relativistic shocks: σ σ σ σ is constant (~ 2.2) independent of shock-B inclination (Drury, ‘83) Relativistic shocks: Different story… (e.g. Krymskii ‘77, Bell ’78, Drury ’83 ) Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Note: Facts for non-relativistic shock acceleration • Particles are everywhere in isotropy and the diffusive approximation for solution of the transport equation can apply • Spectral index ( σ) σ) independent of: scattering nature (κ), σ) σ) (κ), (κ), (κ), inclination ( ψ) ψ) ψ) and ψ) strength of magnetic field (B) Concepts are well understood and well studied - they work well as a comparison basis for relativistic studies Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Acceleration time scale & diffusion The acceleration rate wins in competition with the time scale of the energy losses and the escape rate , defining the limit for the possible highest energies to be achieved. Acceleration rate: τ (E)=(E· τ τ τ τ τ τ τ cycle ) / ∆ ∆ E= [3/(V 1 -V 2 ) ]( κ ∆ ∆ κ κ 1 /V 1 + κ κ κ κ 2 /V 2 ) (Drury ’83) κ Confinement distance One cycle: τ τ cycle (E)= (4/c )( κ τ τ κ 1 /V 1 + κ κ κ κ κ κ 2 /V 2 ) Diffusion coefficient: κ || =(1/3) λυ (Quenby & Meli ’05) i.e. Proton 10GeV: κ about 10²² cm²/s � τ cycle about 10 4 sec Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Simulations of relativistic shock acceleration Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
Relativistic shock acceleration: Questions � Is spectral index (σ) universal? Flat or steep? � σ depends on: gamma shock speed, inclination and scattering modes (turbulence of the media) ? � Efficient acceleration � � UHECRs ? � � see: Ellison et al. (1995), Meli & Quenby (2003a,b, 2005), Niemec & Ostrowski (2004), Ellison & Double (2004), Stecker et al. (2007), Meli et al. (2008) Γ = 5 Γ = 5 Γ = 5 Γ = 5 Γ = 20 Γ = 20 Γ = 20 Γ = 20 Γ = 50 Γ = 50 Γ = 50 Γ = 50 ψ = 30 ψ = 30 ψ = 30 ψ = 30 o o o o 1.8 Oblique shocks Scattering : θ < π/4 Athina Meli, Ghent University Seminar Frankfurt University, June 09 2015
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