Active Galactic Nuclei (AGN) Galaxies with peculiar properties: Extremely bright nuclei Variability High-Energy (X-/g-ray) emission Emission lines Polarization Relativistic outflows (jets)

Cosmic Jets and Radio Lobes Many active galaxies show powerful radio jets Hot spots: Energy in the jets is released in interaction with surrounding material Radio image of Cygnus A Material in the jets moves with almost the speed of light (“Relativistic jets”).

Types of radio-loud AGN and AGN Unification Observing direction Cyg A (radio emission) Radio Galaxy: Powerful “radio lobes” at the end points of the jets, where power in the jets is dissipated.

Types of radio-loud AGN and AGN Unification Quasar or BL Lac object (properties very similar to quasars, but no emission lines) Emission from the jet pointing towards us is enhanced (“Doppler boosting”) compared to the jet moving in the other direction (“counter jet”). Observing direction

Blazars Class of AGN consisting of BL Lac objects and gamma-ray bright quasars Rapidly (often intra-day) variable Strong gamma-ray sources Radio jets, often with superluminal motion Radio and optical polarization

Blazar Models Leptonic Models g-q g1 g2 Synchrotron emission Synchrotron emission Relativistic jet outflow with G ≈ 10 Injection, acceleration of ultrarelativistic electrons nFn n Compton emission g-q Qe (g,t) g1 g2 g Leptonic Models nFn Injection over finite length near the base of the jet. n Seed photons: Synchrotron (SSC), Accr. Disk + BLR (EC) Additional contribution from gg absorption along the jet

Blazar Models Hadronic Models g-q g1 g2 Proton-induced radiation mechanisms: Injection, acceleration of ultrarelativistic electrons and protons Relativistic jet outflow with G ≈ 10 nFn g-q Qe,p (g,t) n Proton synchrotron g1 g2 g pg → pp0 p0 → 2g pg → np+ ; p+ → m+nm m+ → e+nenm Synchrotron emission of primary e- → secondary m-, e-synchrotron nFn Hadronic Models Cascades … n

Fitting the spectral variability of BL Lac in 2000 Linj = 3*1040 erg/s g1 = 1100 g2 = 4*104 → 5*104 q = 2.6 → 2.2 D = 17 eB = 1 B = 1.4 G RB = 2.5*1015 cm Electron acceleration up to ~ 25 GeV (~ TeV in some blazars) Electron injection index q = 2.2 → Relativistic parallel shocks? B = 1.4 G Böttcher & Reimer (2004)

Spectral modeling results along the Blazar Sequence High-frequency peaked BL Lac (HBL): Synchrotron No dense circumnuclear material → No strong external photon field SSC

Spectral modeling results along the Blazar Sequence Radio Quasar (FSRQ) External Compton Plenty of circumnuclear material → Strong external photon field Synchrotron Hartman & Boettcher (2001)