Broadband Properties of BlazarsMarkus Böttcher

Ohio University, Athens, OH, USA

• Phenomenology of Blazars• Recent Observational Results on 3C66A and 3C279• Models of Blazar Emission

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

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)

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)

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

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)

• 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

• 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

• 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 …

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)

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 …

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

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.)

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

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

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

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!

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.

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