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Juri Poutanen University of Oulu, Finland (Stern, Poutanen, 2006, MNRAS, 372, 1217;

A new particle acceleration mechanism and the emission from relativistic jets. Juri Poutanen University of Oulu, Finland (Stern, Poutanen, 2006, MNRAS, 372, 1217; Stern, Poutanen, 2007, MNRAS, submitted, astro-ph/0709.3043). Jet in M87 discovered by Curtis in 1918.

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Juri Poutanen University of Oulu, Finland (Stern, Poutanen, 2006, MNRAS, 372, 1217;

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  1. A new particle acceleration mechanism and the emission from relativistic jets Juri Poutanen University of Oulu, Finland (Stern, Poutanen, 2006, MNRAS, 372, 1217; Stern, Poutanen, 2007, MNRAS, submitted, astro-ph/0709.3043)

  2. Jet in M87discovered by Curtis in 1918

  3. Radio galaxy Cygnus A Redshift z=0.0565, distance of about 211 Mpc Powered by accretion on to a supermassive black hole

  4. Blazar3C 120 2-20 keV X-rays Marscher A. et al., 2002

  5. Egret image of a blazar 3C 279 VLBA imaging of blazar 0827+243. The apparent speed is 25c. The minimum Lorentz factor of the outflow =25.

  6. Superluminal motion Apparent velocity 

  7. Blazar spectra

  8. Blazar sequence Blazar spectra

  9. Observations • Spectra form the so called blazar-sequence (larger luminosity blazars have softer spectra). • Radiations mechanisms: synchrotron, SSC (synchrotron self-Compton) and ERC (external radiation Compton, e.g. broad emission line region photons) • In low-power: SSC b) In high-power: ERC • High-energy emitting electrons: • In low-powers objects “injection” betweenmin=104-105 and max=106-107(Ghisellini et al. 2002, Krawczynski et al. 2002, Konopelko et al. 2003, Giebels et al. 2007). • In high-luminosity minis smaller (but obtained by fitting the low-energy synchrotron peak). • Rapid variability (TeV vary on time-scales down to 3 min in PKS 2155-304; Aharonian et al. 2007)=> small size.

  10. Questions • Energy dissipation site? Broad-line region? Dusty torus? Vicinity of the accretion disk? • What is the initial jet composition: Poynting flux, e–-p, or e–-e+ ? • What is the composition in the active region? • Energy dissipation mechanism? • Jet power? Dissipation efficiency? • Acceleration mechanism of high-energy electrons emitting gamma-rays?

  11. Model for a quasar Alan Marscher

  12. Models • Internal shocks within the outflow: low efficiency (dissipation of internal energy), unless large amplitude oscillations of Lorentz factors are invoked (Beloborodov 2000). • Shear flow/relativistic shock models: • assume some particle scattering law  particle acceleration • If instead reasonable magnetic fluctuation are assumed  there is no particle acceleration (Niemiec & Ostrowski 2006). • Self-consistent computations of magnetic fields in relativistic magnetized flows  no particle acceleration (Spitkovsky). • Magnetic reconnection in magnetically dominated flow? No viable model from first principles yet.

  13. Doppler factor (Delta)-crisis • Doppler factorsdetermined from TeV blazars ~20-50. • Apparent velocitiesat parsec scales in Mrk 421, Mrk 501 are other TeV blazars are mildly relativistic (Marscher 1999; Piner & Edwards 2004, 2005). • Unification (source statistics and luminosity ratio) of FR I with BL Lacs requires ~4÷6 (for the blob and steady jet, respectively). • TeV emission observed in (off-axis) radio galaxy M87 contradicts strong beaming models (predicts huge beamed luminosity). • SOLUTIONS: • Assume decelerating jet (Georganopoulos & Kazanas 2003) • Assume structured jet (fast spine - slow sheath)(Chiaberge et al. 2000, Ghisellini et al. 2005) • Assume large opening angle jet (Gopal-Krishna et al. 2004).

  14. Opacities in AGN jets Thomson depth across the jet is High-energy photons are converted to electron- positron pairs because the optical depth is large Disk T=5 eV Isotropic: BLR Dust =E/mec2 Pairs in the jet are produced with = min=104.5-mirrors the disk spectrum max=106-8 -depends on the magnetic field and the soft photon field.

  15. Photon breeding Breeding:The process by which an organism produces others of its kind: multiplication, procreation, reproduction. Photon breeding is similar to neutron breeding in a nuclear reactor. Photon number and energy density increases exponentially. Energy is taken from the bulk jet energy.

  16. Photon breeding in jet’s shear flow B-field The mechanism is supercritical if the total amplification factor through all the steps is larger than unity: where Cn denote the energy transmission coefficient for a given step. 2 3. Compton scattering 2. Pair production 1. Seed high-energy photon 5. Compton scattering 4. Pair production

  17. Photon breeding in jet’s shear flow B-field Requirements • Some seed high-energy photons • Transversal or chaotic B-field • Isotropic radiation field (broad emission line region at 1017 cm) • Jet Lorentz factor 4(more realistically10). 2 3. Compton scattering 2. Pair production 1. Seed high-energy photon 5. Compton scattering 4. Pair production

  18. Origin of seed high-energy photons Start from the extragalactic gamma-ray background observed at Earth. Luminosity grows by 20 orders of magnitude in 3 years.

  19. Temporal variability Chaotic behaviour?

  20. Gamma-ray emission sites • Internal shock model “predicts” distances How to predict R0? • Photon breeding needs soft (isotropic) photon background. • Near the accretion disk (if the jet is already accelerated with 10) • Broad emission line region at 1017 cm. • Dusty torus at parsecscale (if still 10). • Stellar radiation at kpc scale (if 10). • Cosmic microwave background at 100 kpc scale (if 10).

  21. Electron distribution (in the jet) Ljet=Ldisk=1046erg/s Cooling pairs Pair cascade Ldisk=1044erg/s Ljet=Ldisk=5 1043erg/s Ldisk=5 1043erg/s Photon breeding: electrons are “injected” at >104.5 Observations: the electron “injection” peaks between min=104-105andmax=106-107

  22. Blazar spectra Modeled Observed Gamma-rays

  23. Jet structure 1. Photon breeding provides friction between the jet and the external medium. 2. This results in a decelerating and “structured” jet.

  24. Terminal jet Lorentz factor 1. Terminal Lorentz factor is smaller for larger initial j 2. High radiative efficiency 10-80%. 3. Gradient of  implies broad emission pattern. Cylindrical radius

  25. Angular distribution of radiationfrom the decelerating structured jet Gamma-ray radiation is coming from the fast spine. Optical is synchrotron from the slow sheath. X-rays are the mixture. Gamma-ray at large angles by pairs in external medium have luminosity j4smaller than that at angle 1/j (j2 -amplification, j2 - beaming). Compare to 3ratio for =1/j and ≈1 which is j6 Photon breeding predicts high gamma-luminosity in radio galaxies (e.g. M87). Solves the delta-crisis. Jet optical External medium X-rays -rays SSC ERC

  26. Conclusions • Photon breeding mechanismis based on well-known physics. • Photon breedingis an efficient accelerator of high-energy electrons (pairs). • High radiative efficiency. • Photon breedingproduces decelerating, structured jet. This results in a broad emission pattern. Predicts strong GeV-TeV emission for off-axis objects (radio galaxies). • The process is very promising in explaining high luminosities of relativistic jets in quasars.

  27. Future Self-consistent MHD simulations of the jet acceleration by the magnetic fields near a supermassive black hole together with the jet emission.

  28. Jet and accretion disk

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