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
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Active Galactic Nuclei (AGN)Galaxies with peculiar properties:
• Extremely bright nuclei
• Variability
• High-Energy (X-/-ray) emission
• Emission lines
• Polarization
• Relativistic outflows (jets)
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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
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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
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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
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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
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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
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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 …
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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
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Spectral modeling results along the Blazar Sequence
High-frequency peaked BL Lac (HBL):
No dense circumnuclear material → No strong external
photon field
SynchrotronSSC
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Spectral modeling results along the Blazar Sequence
Radio Quasar (FSRQ)
Plenty of circumnuclear
material → Strong external
photon field
SynchrotronExternal Compton
Hartman & Boettcher (2001)