Transcript Modeling the Spectral Energy Distributions and Variability

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:
Radio image of
Cygnus A
Material in the jets moves
with almost the speed of
light (“Relativistic jets”).
Energy in the jets is
released in interaction
with surrounding
material
Types of radio-loud AGN and
AGN Unification
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”).
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
Synchrotron
emission
Qe (g,t)
Injection,
acceleration of
ultrarelativistic
electrons
nFn
Relativistic jet outflow with G ≈ 10
n
Compton
emission
g1
g2 g
Injection over finite
length near the
base of the jet.
Additional contribution from
gg absorption along the jet
Leptonic
Models
nFn
g-q
n
Seed photons:
Synchrotron (SSC),
Accr. Disk + BLR (EC)
Protoninduced
radiation
mechanisms:
Relativistic jet outflow with G ≈ 10
nFn
Qe,p (g,t)
Injection,
acceleration of
ultrarelativistic
electrons and
protons
Blazar Models
g-q
g1
n
• Proton
synchrotron
g2 g
• pg → pp0
p0 → 2g
• pg → np+ ; p+ → m+nm
nFn
Synchrotron
emission of
primary e-
n
m+ → e+nenm
Hadronic
Models
→ secondary m-,
e-synchrotron
• Cascades …
Fitting the spectral variability
of BL Lac in 2000
• 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):
No dense
circumnuclear
material → No
strong external
photon field
Synchrotron
SSC
Spectral modeling results
along the Blazar Sequence
Radio Quasar (FSRQ)
Plenty of
circumnuclear
material →
Strong external
photon field
Synchrotron
External
Compton
Hartman & Boettcher (2001)