active galactic nuclei (agn)
DESCRIPTION
0. Active Galactic Nuclei (AGN). Galaxies with peculiar properties:. Extremely bright nuclei. Variability. High-Energy (X-/ g -ray) emission. Emission lines. Polarization. Relativistic outflows (jets). 0. Cosmic Jets and Radio Lobes. Many active galaxies show powerful radio jets. - PowerPoint PPT PresentationTRANSCRIPT
Active Galactic Nuclei (AGN)Galaxies with peculiar properties:
• Extremely bright nuclei
• Variability
• High-Energy (X-/-ray) emission
• Emission lines
• Polarization
• Relativistic outflows (jets)
Cosmic Jets and Radio LobesMany active galaxies show powerful radio jets
Radio image of Cygnus A
Material in the jets moves with almost the speed of light (“Relativistic jets”).
Hot spots:
Energy in the jets is released in interaction
with surrounding material
Radio Galaxy:
Powerful “radio lobes” at the end points of the jets, where power in the
jets is dissipated.
Cyg A (radio emission)
Types of radio-loud AGN and AGN Unification
Observing direction
Emission from the jet pointing towards us is enhanced
(“Doppler boosting”) compared to the jet moving in the other
direction (“counter jet”).
Types of radio-loud AGN and AGN Unification
Quasar or BL Lac object (properties very similar to
quasars, but no emission lines)
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 ModelsRelativistic jet outflow with ≈ 10
Injection, acceleration of ultrarelativistic
electrons
Qe (,
t)
Synchrotron emission
F
Compton emission
F
-q
Seed photons:
Synchrotron (SSC), Accr. Disk + BLR (EC)
Injection over finite length near the base of the jet.
Additional contribution from absorption along the jet
Leptonic Models
Blazar ModelsRelativistic jet outflow with ≈ 10
Injection, acceleration of ultrarelativistic electrons and
protons
Qe
,p (,
t)
Synchrotron emission of primary e-
F
Proton-induced radiation
mechanisms:
F
-q
• Proton synchrotron
Hadronic Models
• p → p0 0 → 2
• p → n+ ; + → +
→ e+e
→ secondary -, e-synchrotron
• Cascades …
Fitting the spectral variability of BL Lac in 2000
Böttcher & Reimer (2004)
• Electron acceleration up to ~ 25 GeV
(~ TeV in some blazars)
• Electron injection index q = 2.2
→ Relativistic parallel shocks?
• B = 1.4 G
Spectral modeling results along the Blazar Sequence
High-frequency peaked BL Lac (HBL):
No dense circumnuclear material → No strong external
photon field
SynchrotronSSC
Spectral modeling results along the Blazar Sequence
Radio Quasar (FSRQ)
Plenty of circumnuclear
material → Strong external
photon field
SynchrotronExternal Compton
Hartman & Boettcher (2001)