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
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