Broadband Properties of Blazars
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Broadband Properties of BlazarsMarkus Böttcher
Ohio University, Athens, OH, USA
• Phenomenology of Blazars• Recent Observational Results on 3C66A and 3C279• Models of Blazar Emission
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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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The Blazar Sequence
Flat-Spectrum Radio Quasars:
Low-frequency component from radio to optical/UV
High-frequency component from X-rays to -rays, often dominating total power
Peak frequencies lower than in BL Lac objects
Collmar et al. (2006)High-frequency peaked
BL Lacs (HBLs):
Low-frequency component from radio to UV/X-rays, often
dominating the total power
High-frequency component from hard X-rays to high-
energy gamma-rays
Low-frequency peaked BL Lacs (LBLs):
Peak frequencies at IR/Optical and GeV gamma-rays
Intermediate overall luminosity
Sometimes -ray dominated
(Boettcher & Reimer 2004)
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RXTE
Radio obs. by
UMRAO (Univ. of Michigan),
Metsähovi (Finland),
VLBA,
IR observations by
Mt. Abu (India)
NOT (Canary Islands),
Campo Imperatore (Italy)
Optical observations by the WEBT collaboration:
24 observatories in 15 countries around the
world
X-ray obs. by RXTE
Very-high-energy gamma-ray obs. by
Whipple/VERITAS (Arizona),
STACEE (New Mexico)
VHE
The Multiwavelength Campaign on 3C66A
(Böttcher, et al., 2005)
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Broadband Spectral Energy DistributionsSynchrotron
peak at optical wavelengths
Synchrotron emission extends far into the X-ray
regime (> 10 keV)
Estimates from spectrum and variability:
Variability → Size: Rb ~ 2.2*1015 D1 cm Synchrotron luminosity → B ~ 4.4 D1
-1 G Synchrotron spectral index → Electron injection index q ~ 3
Synchrotron peak frequency → e,min ~ 3.1*103 → Particle acceleration at non-parallel shocks
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Radio Observations
Rather smooth jet without
clearly visible knots
Identification of 7 jet
components
Evidence for superluminal motion in only one component:
vapp = (12 ± 8.0) c
Decay of Brightness Temperature TB with
distance d from the core:
TB ~ d-2 → B ~ d-1
Predominantly perpendicular magnetic field!
(T. Savolainen)
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• INTEGRAL + Chandra ToO observations
• Coordinated with WEBT radio, near-IR, optical (UBVRIJHK)
• Triggered by Optical High State (R < 14.5) on Jan. 5, 2006
• Addl. X-ray Observations by Swift XRT
The Multiwavelength Campaign on 3C279 in Jan./Feb. 2006
Preliminary
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• X-ray/-ray observations during a period of optical-IR-radio decay
The Multiwavelength Campaign on 3C279 in Jan./Feb. 2006
• Minimum at X-rays seems to precede optical/radio minimum by ~ 1 day.
Preliminary
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• SED (Jan 15, 2006) basically identical to low states in 92/93 and 2003 in X-rays
• High flux, but steep spectrum in optical
• Indication for cooling off a high state?
• Did we miss the HE flare?
The Multiwavelength Campaign on 3C279 in Jan./Feb. 2006
Analysis is in progress …
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Blazar ModelsRelativistic jet outflow with ≈ 10
Injection, acceleration of ultrarelativistic
electrons
Qe (,
t)
Synchrotron emission
F
Compton emission
F
-q
Injection over finite length near the base of the jet.
Additional contribution from absorption along the jet
Leptonic Models
Seed photons:
Synchrotron (within same region [SSC] or slower/faster earlier/later emission regions
[decel. jet]), Accr. Disk, BLR, dust torus (EC)
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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
Hadronic Models
• Proton synchrotron
• p → p0 0 → 2
• p → n+ ; + → +
→ e+e
→ secondary -, e-synchrotron
• Cascades …
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Modeling of 3C66A in 2003-2004Time-dependent broadband SED
(Joshi & Böttcher 2006, in prep.)
Model parameters:
D = = 24
RB = 3.6*1015 cm
B = 2.4 G
q = 3.1 → 2.4
2 = 3.0*104 → 4.5*104
Linj = 2.7*1041 erg/s → 7.0*1041 erg/s
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Modeling of 3C66A in 2003-2004R-band (optical) light curveModel parameters:
D = = 24
RB = 3.6*1015 cm
B = 2.4 G
q = 3.1 → 2.4
2 = 3.0*104 → 4.5*104
Linj = 2.7*1041 erg/s → 7.0*1041 erg/s
Hardening of injection spectrum during flare; increase
of high-energy cut-off → Flaring caused by changing magnetic-field orientation? (Joshi & Böttcher 2006, in prep.)
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Spectral modeling results along the Blazar Sequence: Leptonic Models
High-frequency peaked BL Lac (HBL):
SynchrotronSSC
Low magnetic fields (~ 0.1 G);
High electron energies (up to TeV);
Large bulk Lorentz factors ( > 10)
No dense circumnuclear material → No strong external
photon field
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Spectral modeling results along the Blazar Sequence: Leptonic Models
Radio Quasar (FSRQ)
SynchrotronExternal Compton
High magnetic fields (~ a few G);
Lower electron energies (up to GeV);
Lower bulk Lorentz factors ( ~ 10)
Plenty of circumnuclear material → Strong
external photon field
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Spectral modeling results along the Blazar Sequence: Hadronic ModelsHBLs: Low co-moving synchrotron photon energy density;
high magnetic fields; high particle energies
→ High-Energy spectrum dominated by featureless proton synchrotron initiated cascades, extending to
multi-TeV, peaking at TeV energies
LBLs: Higher co-moving synchrotron photon energy density; lower magnetic fields;
lower particle energies
→ High-Energy spectrum dominated by p pion decay, and synchrotron-initiated
cascade from secondaries
→ multi-bump spectrum extending to TeV energies, peaking at GeV energies
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The Blazar Sequence
NOT a prediction of leptonic or hadronic jet models!
Variations of B, <>, , … chosen as free parameters in order to fit individual objects along the blazar sequence.
Consistent prediction: Strong > 100 GeV
emission from LBLs, FSRQs are only
expected in hadronic models!
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Summary
1. Blazar SEDs successfully be modelled with both leptonic and hadronic jet models.
2. Possible multi-GeV - TeV detections of LBLs or FSRQs and spectral variability may serve as diagnostics to distinguish between models.
3. Both leptonic and hadronic models provide plausible scenarios for explaining the blazar sequence, but the blazar sequence is not a prediction of either type of models.
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Time-dependent leptonic blazar modeling
Solve simultaneously for evolution of electron distribution,
and co-moving photon distribution,
= - ( ne) + Qe (,t) - ______ __∂ne (,t)
∂t∂
∂.
rad. + adiab. losses escape
______ne (,t)tesc,e
= nph,em (,t) – nph,abs (,t) - _______∂nph (,t)
∂t.
Sy., Compton emission escape
______nph (,t)tesc,ph
SSA, absorption
.
el. / pair injection