Modeling the Emission Processes in Blazars

Markus Böttcher

Ohio University

Athens, OH

Outline

• Leptonic and Hadronic Models of Blazars

• Recent Modeling Results

• Hybrid Leptonic/Hadronic Blazar Models and “Orphan” TeV Flares

• Recent Observational Results on 3C279

Blazar ModelsRelativistic jet outflow with ≈ 10

Injection, acceleration of ultrarelativistic

electrons

Qe (,

t)

Synchrotron emission

F

Compton emission

F

-q

Seed photons:

Synchrotron (within same region [SSC] or slower/faster earlier/later emission regions

[decel. jet]), Accr. Disk, BLR, dust torus (EC)

Injection over finite length near the base of the jet.

Additional contribution from absorption along the jet

Leptonic Models

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 …

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

Spectral modeling results along the Blazar Sequence: Leptonic Models

High-frequency peaked BL Lac (HBL):

No dense circumnuclear material → No strong external

photon field

SynchrotronSSC

Low magnetic fields (~ 0.1 G);

High electron energies (up to TeV);

Large bulk Lorentz factors ( > 10)

Spectral modeling results along the Blazar Sequence: Leptonic Models

Radio Quasar (FSRQ)

Plenty of circumnuclear

material → Strong external

photon field

SynchrotronExternal Compton

High magnetic fields (~ a few G);

Lower electron energies (up to GeV);

Lower bulk Lorentz factors ( ~ 10)

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 an a-priori 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!

Example: Modeling SEDs and Variability of BL Lacertae in 2000

Modeling of SEDs in X-ray low and high state

Böttcher & Reimer (2004)

Analytical parameter estimates• SL motion up to app ~ 7.1 => > 8~

• Optical/X-ray variability => RB < 1.6*1015 D1 cm~

• Synchrotron peak flux => Bsy ≈ 3.6 D1-1 B

2/7 G

• Optical – X-ray time delay => BRX ≈ 1.6 D1-1/3 -2/3 G

(where = uext/uB)=> B ~ 2 G

• Location of synchrotron peak => <> ~ 1.4*103 D1-1/2

• Location of synchrotron cutoff =>2 ~ 4*104 D1

-1/2 (qu.)

2 ~ 2*105 D1-1/2 (act.)

• Total luminosity => Lj,e > 1041 D1

-4 erg/s (in electrons only)~

Fitting the spectral variability of BL Lac in 2000

Linj = 3*1040 erg/s

1 = 1100

2 = 4*104 → 5*104

q = 2.6 → 2.2

D = 17

B = 1

B = 1.4 G

RB = 2.5*1015 cm

Fit to X-ray hardness-intensity diagrams

Fit to color-magnitude correlation

Best fit to spectrum and variability for

flaring scenario with electron injection

spectrum hardening during flare

Possible physical interpretation:

Change in magnetic-field orientation with

respect to shock front in the jet (?)

Comparison to Hadronic Model

Parameters of synchrotron-proton

blazar model fit

(A. Reimer):

D = 7

RB = 1.1*1015 cm

B = 40 G

e = p = 1.8

ne/np = 1.6

p,max = 7*109

High-energy emission dominated

by -synchrotron

Hadronic processes => Detectable in > 100 GeV – TeV gamma-rays

Conclusions for BL Lac, if hadronic models could be ruled out:

Linj = 3*1040 erg/s

1 = 1100

2 = 4*104 → 5*104

q = 2.6 → 2.2

D = 17

B = 1

B = 1.4 G

RB = 2.5*1015 cm

• Electron acceleration out to ~ 25 GeV during flares

• Particle injection index 2.2, consistent with acceleration at relativistic, parallel shocks

• Magnetic field in equipartition with ultrarelativistic electron population

The Case of 1ES 1959+650

• HBL at z = 0.047• TeV source• Recently displayed

an “Orphan” TeV flare

0 4020 8060

Date [MJD-52400]

(Krawczynski et al. 2004)

Primary sy + -ray flare

Secondary -ray flare w/o sy flare

Clearly unexpected in purely leptonic one-zone SSC models

Relativistic hadrons in leptonic jets

• Naturally expected in any realistic particle acceleration scenario

• For standard hadronic models:p,max ~ 108 required (p pion production on co-moving synchrotron photons) to work (p*Eph > 300 MeV)

• But:p pion production on external photons possible for much lower proton Lorentz factors (p ~ 103 – 104)

→ Synchrotron mirror model for p pion production

The Hadronic Synchrotron Mirror Model

Constraint on Rm from time delay:

Rm ~ 3 12 t20 pc

m = 0.1 -1

= 10 1

t = 20 t20 d

The Hadronic Synchrotron Mirror Model

Estimate of reflected synchrotron photon density from Rm and

observed primary synchrotron flare

u’sy ~ 6.0x10-3 1-4 R16

-2 ergs cm-3

Dominant contribution to p pion production from protons with

p ~ 3,000 1-1 Esy,1

-1

Esy ~ 10 keV

Normalization of 0 decay flare to observed secondary TeV flare

Constraint on co-moving relativistic proton density:

n’p ~ 1.8x107 1-3 Esy,1 r17 -1

-1 R16-2 cm-3

Reflected sy. photons are virtually invisible to ultrarel. electrons

(Klein-Nishina)

The Hadronic Synchrotron Mirror Model

Kinetic luminosity in relativistic protons in the jet:

Lkinp ~ 1.8x1048 Esy,1 R16

-2 r17 -

1-1 f-3 ergs/s

Optical – soft X-ray synchrotron flare from + decay products:

m ~ 0.05 mag

Neutrino emission from charged pion decay unlikely to be

detectable with current detectors (Reimer et al. 2005)

Some New Observational Results:

• 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 …

Summary1. Blazar SEDs successfully be modelled with both

leptonic and hadronic jet models. 2. Blazar Sequence is NOT a prediction of either

type of models.3. Possible multi-GeV - TeV detections of LBLs or

FSRQs and spectral variability may serve as diagnostics to distinguish between models.

4. Even in leptonically dominated models, relativistic hadrons might be present

5. One possible diagnostic for relativistic hadrons: Orphan TeV flares without simultaneous synchrotron flare.

Spectral Variability Signatures

2 = 2*104 → 4*104

q = 2.5 → 2.3

Linj,e = 2.5*1040 erg/s → 3.5*1040 erg/s

2 = 2*104 → 4*104

q = 2.5 → 2.3

(Linj,e adjusted so that dNinj,e/dt = const.)

=> Variability dominated by changing q is a good candidate!

Modeling the SEDs of BL Lac in 2000 Linj = 4*1040 erg/s

1 = 1100

2 = 6*104

q = 2.15

D = 18

B = 0.5

B = 1.4 G

RB = 2.5*1015 cm

Linj = 3*1040 erg/s

2 = 2.3*104

q = 2.4

D = 16