Can short variability time scales be reconciled with

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

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

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

AUGER claims correlation of UHE events with positions of AGN with Distances < 75 Mpc Faraday rotation: BLSC ~ 0. 3 m. G (Valleé 2002) Large deflection angles! variability across the electromagnetic spectrum, Palaiseau, 22 -26, 2008 Likewise in. Blazar other superclusters, e. g. Coma SCApril(Kim et al. 2004)

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

Supergalactic cosmic rays • Cosmic ray storage in Local Supercluster (tesc > t. H) • 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. 3 m. G 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

Supergalactic neutrinos Mannheim & Elsässer 2008 Colafrance sco & Blas i 1999 Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008

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

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 photoproduction of secondaries (Bethe-Heitler pairs, pions) – Largest cosmological emissivity among „Hillas-allowed“ sources Opacities of pg and gg linked, i. e. Te. V 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

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

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

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

Mannheim et al. 1996 Steady-state PIC including proton synchrotron and BH pairs: Variety of SEDs Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008

Variable PIC blazar emission: Quasi-equilibrium spectra with viewing angle varying by a few degrees (Mkn 421) Higher photon compactness (short variability time scales) Broken power-law spectra with „universal“ VHE spectrum a ~ 2 ao Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008

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

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. 1 pc. Maybe. Blazar finevariability structure atelectromagnetic 0. 01 pc to explain VHE across the spectrum, Palaiseau, Aprilvariability? 22 -26, 2008

Parameter space for cooling mechanisms nc sy n- uo M Synchrotron n ro ot hr Photohadronic s re fla Adiabatic Rachen 2001 Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008

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

Can short time scales be reconciled with hadronic emission models? (Cf. Begelman et al. 2007) • • VHE Flares (Mkn 501; PKS 2155 -304) exhibit tvar ~ 300 s Adiabatic loss time tp ~ Gtvar ~ 3 103 G 10 s Larmor time t. L ~ 103 B 2 -1 g 9 s Photomeson cooling time tp ~ 103 x-2 -1 B 2 -2 g 9 -1 s where x = urad / u. B (assuming a=1 down to threshold), and this further yields Liso ~ 1046 B 24 x-2 g 9 erg/s • Pair production cooling time scale for gamma rays tgg ~ 103 x-2 -1 B 2 -2 G 10 (E 0. 1 Te. V)-1 s affirmative! Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008

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 (a. E/m 8)1/2 r-1 where m 8=(M/108 M 8), a. E denotes the accretion rate in units of the Eddington rate, and r the jet diameter in units of the Scharzschild radius • Canonical values adopting m 8=1 and a. E=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

Observational challenge: Need synchrotron-self-absorption turnover frequency measurements of flaring components to infer magnetic field: Scaling: nt ~ 1013 G 10 (r/1015 cm)-1 Hz Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008

Example 1: 1 ES 1218+304 What do SSC model fits of blazar SEDs tell us about the magnetic field? (Examples from M. Meyer, Ph. D thesis 2008) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008

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

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

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

However, the tendency of VHE detected blazars to show two peaks of almost equal luminosity implies that urad ~ u. B 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 m. Jy) Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008

Conclusions Pros • • Cons 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) • 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 Ge. V) • Perhaps problems with circular radio polarization (Wardle et al. , Nature) due s e i c to low-energy end of proton uen q Flatter VHE spectra consistent fwith e r e population ? ver m i de-absorbed observedurspectra o g n e t dr ewith e r v (whereas SSC/EC models fight a r f e n -i bs msteepening). f. ! KN and pair. Oproduction • Ions suffer photo-desintegration m b m u r s e f in n during acceleration ? to i Obtain UHE cosmic ray protons (from escaping neutrons) • Time-dependent code, including all relevant threshold effects and radiative channels, not yet available Blazar variability across the electromagnetic spectrum, Palaiseau, April 22 -26, 2008