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

2 Jet in M87 discovered by Curtis in 1918

3 Radio galaxy Cygnus A 1.Redshift z=0.0565, distance of about 211 Mpc 2.Powered by accretion on to a supermassive black hole

4 Blazar 3C keV X-rays Marscher A. et al., 2002

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

6 Apparent velocity  Superluminal motion

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) a)In low-power: SSC b) In high-power: ERC High-energy emitting electrons: a)In low-powers objects “injection” between  min = and  max = (Ghisellini et al. 2002, Krawczynski et al. 2002, Konopelko et al. 2003, Giebels et al. 2007). b)In high-luminosity  min is smaller (but obtained by fitting the low-energy synchrotron peak). Rapid variability (TeV vary on time-scales down to 3 min in PKS ; 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  Alan Marscher Model for a quasar

12 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: a)assume some particle scattering law  particle acceleration b)If instead reasonable magnetic fluctuation are assumed  there is no particle acceleration (Niemiec & Ostrowski 2006). c)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. Models

13 Doppler factors determined from TeV blazars ~ Apparent velocities at 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: a)Assume decelerating jet (Georganopoulos & Kazanas 2003) b)Assume structured jet (fast spine - slow sheath) (Chiaberge et al. 2000, Ghisellini et al. 2005) c)Assume large opening angle jet (Gopal-Krishna et al. 2004). Doppler factor (Delta)-crisis

14 Opacities in AGN jets High-energy photons are converted to electron- positron pairs because the optical depth is large Thomson depth across the jet is Disk T=5 eV Isotropic: BLR Dust =E/mec2=E/mec2 Pairs in the jet are produced with  =   min = mirrors the disk spectrum  max = 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 The mechanism is supercritical if the total amplification factor through all the steps is larger than unity: where C n denote the energy transmission coefficient for a given step. Photon breeding in jet’s shear flow 22 5. Compton scattering 4. Pair production 3. Compton scattering 2. Pair production 1. Seed high- energy photon B -field

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

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

19 Temporal variability Chaotic behaviour?

20 Gamma-ray emission sites Internal shock model “predicts” distances How to predict R 0 ? Photon breeding needs soft (isotropic) photon background. 1.Near the accretion disk (if the jet is already accelerated with   10 ) 2.Broad emission line region at cm. 3.Dusty torus at parsec scale (if still   10 ). 4.Stellar radiation at kpc scale (if   10 ). 5.Cosmic microwave background at 100 kpc scale (if   10 ).

21 Electron distribution (in the jet) L disk = erg/s L disk =10 44 erg/s L jet =L disk = erg/s Pair cascade Cooling pairs Photon breeding: electrons are “injected” at  > Observations: the electron “injection” peaks between  min = and  max = L jet =L disk =10 46 erg/s

22 Blazar spectra Gamma-rays Observed Modeled

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 radiation from the decelerating structured jet 1.Gamma-ray radiation is coming from the fast spine. 2.Optical is synchrotron from the slow sheath. 3.X-rays are the mixture. 4.Gamma-ray at large angles by pairs in external medium have luminosity  j 4 smaller than that at angle 1/  j (  j 2 -amplification,  j 2 - beaming). Compare to  3 ratio for  = 1/  j and  ≈1 which is  j 6 5.Photon breeding predicts high gamma-luminosity in radio galaxies (e.g. M87). 6.Solves the delta-crisis. optical X-rays  -rays ERC SSC Jet External medium

26 Conclusions Photon breeding mechanism is based on well- known physics. Photon breeding is an efficient accelerator of high-energy electrons (pairs). High radiative efficiency. Photon breeding produces 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