1 / 28

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.

mahon
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related