Can short variability time scales be reconciled with hadronic emission?

1. Can short variability time scales be reconciled with hadronic emission? Karl Mannheim Institut für Theoretische Physik und Astrophysik Universität Würzburg Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

2. Outline • Proton and ion acceleration in the light of recent AUGER results • Proton driven radiation • Variability in hadronic emission models • Do we know enough about the magnetic field? • Conclusions Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

3. Supergalactic anisotropy arising for cosmic rays above the GZK energy (by chance, the GHK horizon corresponds to the dimension of the Local Supercluster ~ 50 Mpc) Local Supercluster Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

4. AUGER claims correlation of UHE events with positions of AGN with Distances < 75 Mpc Faraday rotation: BLSC ~ 0.3 mG (Valleé 2002)  Large deflection angles! Likewise in other superclusters, e.g. Coma SC (Kim et al. 2004) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

5. Constrained simulations of the Local Supercluster (Klypin et al. 2001, 2007) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

6. Supergalactic cosmic rays • Cosmic ray storage in Local Supercluster (tesc > tH) • Anisotropy in the outskirts of the Local Supercluster (Local Group) • Energy density build up from past „shock acceleration“ activity • Jets and hot spots from radio galaxies • Accretion disk winds from Seyferts • Superwinds from Starburst galaxies • Shocks from colliding galaxies • Merger shocks in clusters of galaxies • Accretion shocks from structure formation • Gamma Ray Bursts !! Collisionless shocks go along with Weibel instability  magnetic field !! • Equipartition magnetic field B ~ 0.3mG infered from observed UHE flux • Mean spectral index of radio galaxies in Local Supercluster (-2.4) • Neutrino emission due to pp-collisions at level detectable by ICECUBE (In addition, there must be neutrino emission from the sources) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

7. Supergalactic neutrinos Mannheim & Elsässer 2008 Colafrancesco & Blasi 1999 Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

8. Limit on the extragalactic neutrino flux from photo-hadronic sources(Mannheim, Protheroe, & Rachen 2000) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

9. Protons and ions radiative agents in blazars? • Stochastic acceleration in supergalactic medium too slow • Composition favors (CNO) enriched environment (Dermer 2007) • Pressure equilibrium of radio jets with intracluster medium requires baryons in the nonthermal plasma • DSA favors heavy particles: • Large gyro-radii help crossing nonlinearly broadened shocks • Particles in Maxwell tail can interact resonantly with Alvén waves (efficient injection from thermal pool) • Turbulent power spectra speed up diffusion of large-gyroradius particles (more power at small k) • Reach ultrahigh energies before energy losses become important • Energy losses due to synchrotron emission and photo-production of secondaries (Bethe-Heitler pairs, pions) • Largest cosmological emissivity among „Hillas-allowed“ sources Opacities of pg and gg linked, i.e. TeV blazars optically thin for UHE cosmic rays (Mannheim 1993, Waxman-Bahcall 1999) • Gamma-ray emitting blazars (radio galaxies) thus prime candidates for UHE CR acceleration (Biermann & Strittmatter 1987, Mannheim & Biermann 1992, Rachen & Biermann 1993) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

10. Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

11. Proton-initiated unsaturated electromagnetic cascades Stationary solution from applying Banach‘s fixed point theorem to the equivalent Volterra-type integro-differential equation of type II (Mannheim, Krülls, & Biermann 1991) Note: No diffusion term, no spatial gradients (but finite size of emission region) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

12. Steady-state PIC emission: Hot spots of FR-II radio galaxies as sources of UHE cosmic rays (MKB 1991) Low photon compactness  structured VHE spectra Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

13. Mannheim et al. 1996 Steady-state PIC including proton synchrotron and BH pairs: Variety of SEDs

14. Variable PIC blazar emission: Quasi-equilibrium spectra with viewing angle varying by a few degrees (Mkn421) Higher photon compactness (short variability time scales)  Broken power-law spectra with „universal“ VHE spectrum a ~ 2ao Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

15. Shocks propagating down the jet: Gamma-ray flares when the synchrotron-self-absorption frequency falls below the photo-production threshold pg-threshold Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

16. Distance of gamma-ray emission zone from black hole: SL motion and X-ray (g-ray?) variability in HST-1 indicate nozzle (reonfinement shock) at 106 RS Cheung, Harris, & Stawarcz 2007 Unresolved radio structures down to 0.15 pc. X-ray variability indicates l<0.1pc. Maybe fine structure at 0.01 pc to explain VHE variability? Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

17. Parameter space for cooling mechanisms Synchrotron Muon-synchrotron flares Photohadronic Adiabatic Rachen 2001 Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

18. Muon synchrotron flares Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

19. Can short time scales be reconciled with hadronic emission models? (Cf. Begelman et al. 2007) • VHE Flares (Mkn 501; PKS 2155-304) exhibit tvar ~ 300s • Adiabatic loss time tp ~ Gtvar ~ 3 103G10 s • Larmor time tL ~ 103 B2-1g9 s • Photomeson cooling time tp ~ 103x-2-1B2-2g9-1s where x = urad / uB (assuming a=1 down to threshold), and this further yields Liso ~ 1046 B24x-2g9 erg/s • Pair production cooling time scale for gamma rays tgg ~ 103x-2-1 B2-2G10 (E0.1 TeV)-1 s  affirmative! Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

20. Strong helical magnetic fields • Launching the jet near the light cylinder (Michel 1969) creates highly magnetized, hollow jet with toroidal field • Transverse RM gradients (Gabuzda et al. 2004) • Trajectories of VLBI knots • Morphology • Periodic optical/radio lightcurves • Adiabatically expanding equipartition magnetic field from base of jet can explain measurements across many scales: B [G] ~ 3 104 (aE/m8)1/2 r-1 where m8=(M/108M8), aE denotes the accretion rate in units of the Eddington rate, and r the jet diameter in units of the Scharzschild radius • Canonical values adopting m8=1 and aE=10-2 are Gamma ray emission zone (mpc) 30 G VLBI knots (0.1 pc) 0.3 G Hot Spots (kpc) 3 10-4 G Meisenheimer et al. 1989 Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

21. Observational challenge: Need synchrotron-self-absorption turnover frequency measurements of flaring components to infer magnetic field: Scaling: nt ~ 1013G10 (r/1015cm)-1 Hz Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

22. What do SSC model fits of blazar SEDs tell us about the magnetic field? (Examples from M. Meyer, PhD thesis 2008) Example 1: 1ES1218+304 Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

23. Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

24. What do SSC model fits of blazar SEDs tell us about the magnetic field? (Examples from M. Meyer, PhD thesis 2008) Example 2: 1ES 2344+514 Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

25. SSC models generally favor B ~ 0.2 G at milli-parsec scale (Two orders of magnitude below expectation from adiabatic expansion) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

26. However, the tendency of VHE detected blazars to show two peaks of almost equal luminosity implies that urad ~ uB in SSC models.This equilibrium could make some sense in nonlinear plasma physics.Proton blazar models expected to establish a greater variety of peak luminosity ratios, determined by their proton maximum energy and proton-to-electron ratio (but: could be selection effect, e.g. MAGIC saw only 1/3 of all observed HBLs above 2 mJy) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008

27. Pros Minute time scales ok if magnetic field is of the order of 100 G as required by some electrodynamic jet models (cf. Also optical circular polarization, Wagner et al. SPIE 2000) Doppler factors ~10 consistent with population statistics, avoid increase of energy requirements from increasing the opening angle of the jet (>1/G) Flatter VHE spectra consistent with de-absorbed observed spectra (whereas SSC/EC models fight with KN and pair production steepening) Obtain UHE cosmic ray protons (from escaping neutrons) Cons Acceleration close to Bohm Limit Sensitive to macroscopic structure Variety of flare SEDs at high energies rather than simple generic shape (quiescence: tendency for a~1 steeping to a~2 at ~ 100 GeV) Perhaps problems with circular radio polarization (Wardle et al., Nature) due to low-energy end of proton population ? Ions suffer photo-desintegration during acceleration ? Time-dependent code, including all relevant threshold effects and radiative channels, not yet available Conclusions Observe turnover frequencies in submm-infared regime to infer m.f.! Blazar variability across the electromagnetic spectrum, Palaiseau, April 22-26, 2008