1. Broadband Properties of Blazars
Broadband Properties of Blazars
Markus Böttcher
Ohio University, Athens, OH, USA
Phenomenology of Blazars
Recent Observational Results on 3C66A and 3C279
Models of Blazar Emission

2. 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

3. The Blazar Sequence Low-frequency peaked BL Lacs (LBLs):
Low-frequency peaked BL Lacs (LBLs):
Peak frequencies at IR/Optical and GeV gamma-rays
Intermediate overall luminosity
Sometimes g-ray dominated
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
Flat-Spectrum Radio Quasars:
Low-frequency component from radio to optical/UV
High-frequency component from X-rays to g-rays, often dominating total power
Peak frequencies lower than in BL Lac objects
(Boettcher & Reimer 2004)

4. The Multiwavelength Campaign on 3C66A
Radio obs. by
UMRAO (Univ. of Michigan),
Metsähovi (Finland),
VLBA,
Optical observations by the WEBT collaboration:
24 observatories in 15 countries around the world
IR observations by
Mt. Abu (India)
NOT (Canary Islands),
Campo Imperatore (Italy)
Very-high-energy gamma-ray obs. by
Whipple/VERITAS (Arizona),
STACEE (New Mexico)
VHE
X-ray obs. by RXTE
RXTE
(Böttcher, et al., 2005)

5. Broadband Spectral Energy Distributions
Synchrotron 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
→ Particle acceleration at non-parallel shocks
Synchrotron peak frequency → ge,min ~ 3.1*103

6. Radio Observations Rather smooth jet without clearly visible knots
Rather smooth jet without clearly visible knots
Identification of 7 jet components
(T. Savolainen)
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!

7. The Multiwavelength Campaign on 3C279 in Jan./Feb. 2006
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
Preliminary

8. The Multiwavelength Campaign on 3C279 in Jan./Feb. 2006
X-ray/g-ray observations during a period of optical-IR-radio decay
Preliminary
Minimum at X-rays seems to precede optical/radio minimum by ~ 1 day.

9. The Multiwavelength Campaign on 3C279 in Jan./Feb. 2006
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?
Analysis is in progress …

10. 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)
Leptonic Models
nFn g1 g2 g n
Injection over finite length near the base of the jet.
Seed photons:
Synchrotron (within same region [SSC] or slower/faster earlier/later emission regions [decel. jet]), Accr. Disk, BLR, dust torus (EC)
Additional contribution from gg absorption along the jet

11. 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
Synchrotron emission of primary e-
pg → np+ ; p+ → m+nm
m+ → e+nenm
nFn
Hadronic Models
→ secondary m-, e-synchrotron
Cascades … n

12. Modeling of 3C66A in 2003-2004 Time-dependent broadband SED
Time-dependent broadband SED
Model parameters:
D = G = 24
RB = 3.6*1015 cm
B = 2.4 G
q = 3.1 → 2.4
g2 = 3.0*104 → 4.5*104
Linj = 2.7*1041 erg/s → 7.0*1041 erg/s
(Joshi & Böttcher 2006, in prep.)

13. Modeling of 3C66A in 2003-2004 R-band (optical) light curve
R-band (optical) light curve
Model parameters:
D = G = 24
RB = 3.6*1015 cm
B = 2.4 G
q = 3.1 → 2.4
g2 = 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.)

14. Spectral modeling results along the Blazar Sequence: Leptonic Models
Low magnetic fields (~ 0.1 G);
High electron energies (up to TeV);
Large bulk Lorentz factors (G > 10)
High-frequency peaked BL Lac (HBL):
Synchrotron
SSC
No dense circumnuclear material → No strong external photon field

15. Spectral modeling results along the Blazar Sequence: Leptonic Models
Radio Quasar (FSRQ)
High magnetic fields (~ a few G);
Lower electron energies (up to GeV);
Lower bulk Lorentz factors (G ~ 10)
External Compton
Plenty of circumnuclear material → Strong external photon field
Synchrotron

16. Spectral modeling results along the Blazar Sequence: Hadronic Models
HBLs:
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 pg pion decay, and synchrotron-initiated cascade from secondaries
→ multi-bump spectrum extending to TeV energies, peaking at GeV energies

17. NOT a prediction of leptonic or hadronic jet models!
The Blazar Sequence
NOT a prediction of leptonic or hadronic jet models!
Variations of B, <g>, G, … 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!

18. Summary
Blazar SEDs successfully be modelled with both leptonic and hadronic jet models.
Possible multi-GeV - TeV detections of LBLs or FSRQs and spectral variability may serve as diagnostics to distinguish between models.
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.

20. Time-dependent leptonic blazar modeling
Solve simultaneously for evolution of electron distribution,
∂ne (g,t) .
______ ∂ __
ne (g,t)
______
= (g ne) + Qe (g,t) - ∂t ∂g
tesc,e
rad. + adiab. losses
el. / pair injection
escape
and co-moving photon distribution,
∂nph (e,t) . .
_______
nph (e,t)
______
= nph,em (e,t) – nph,abs (e,t) - ∂t
tesc,ph
Sy., Compton emission
SSA, gg absorption
escape