Modeling the Emission Processes in Blazars

0 Modeling the Emission Processes in Blazars Markus Böttcher Ohio University Athens, OH

0 Outline • Leptonic and Hadronic Models of Blazars • Recent Modeling Results • Hybrid Leptonic/Hadronic Blazar Models and “Orphan” TeV Flares • Recent Observational Results on 3C279

0 Blazar Models Synchrotron emission Relativistic jet outflow with G≈ 10 Injection, acceleration of ultrarelativistic electrons nFn n Compton emission g-q Qe (g,t) g1 g2 g Leptonic Models nFn Injection over finite length near the base of the jet. n 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

0 Blazar Models 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→ pp0p0 →2g • pg→ np+ ; p+ → m+nm • m+→ e+nenm Synchrotron emission of primary e- → secondary m-, e-synchrotron Hadronic Models nFn • Cascades … n

0 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

0 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 No dense circumnuclear material → No strong external photon field SSC

0 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

0 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

0 The Blazar Sequence NOT an a-priori 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!

0 Example: Modeling SEDs and Variability of BL Lacertae in 2000 Böttcher & Reimer (2004) Modeling of SEDs in X-ray low and high state

0 Analytical parameter estimates • SL motion up to bapp ~ 7.1 => G> 8 ~ • Optical/X-ray variability => RB< 1.6*1015 D1 cm ~ • Synchrotron peak flux => Bsy≈ 3.6 D1-1eB2/7 G • Optical – X-ray time delay => BRX≈ 1.6 D1-1/3(1 + k)-2/3 G (where k = uext/uB) =>B ~ 2 G • Location of synchrotron peak => <g> ~ 1.4*103 D1-1/2 g2 ~ 4*104 D1-1/2 (qu.) • Location of synchrotron cutoff => g2 ~ 2*105 D1-1/2 (act.) • Total luminosity => Lj,e > 1041 D1-4 erg/s (in electrons only) ~

0 Fitting the spectral variability of BL Lac in 2000 Linj = 3*1040 erg/s g1 = 1100 g2 = 4*104 → 5*104 q = 2.6 → 2.2 D = 17 eB = 1 B = 1.4 G RB = 2.5*1015 cm

0 Fit to X-ray hardness-intensity diagrams

0 Fit to color-magnitude correlation Best fit to spectrum and variability for flaring scenario withelectron injection spectrum hardeningduring flare Possible physical interpretation: Change in magnetic-field orientation with respect to shock front in the jet (?)

0 Comparison to Hadronic Model Parameters of synchrotron-proton blazar model fit (A. Reimer): D = 7 RB = 1.1*1015 cm B = 40 G ae = ap = 1.8 ne/np = 1.6 gp,max = 7*109 High-energy emission dominated by m-synchrotron Hadronic processes => Detectable in > 100 GeV – TeV gamma-rays

0 Conclusions for BL Lac, if hadronic models could be ruled out: • 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 Linj = 3*1040 erg/s g1 = 1100 g2 = 4*104 → 5*104 q = 2.6 → 2.2 D = 17 eB = 1 B = 1.4 G RB = 2.5*1015 cm

0 The Case of 1ES 1959+650 Primary sy + g-ray flare Secondary g-ray flare w/o sy flare • HBL at z = 0.047 • TeV source • Recently displayed an “Orphan” TeV flare (Krawczynski et al. 2004) Clearly unexpected in purely leptonic one-zone SSC models 0 20 40 60 80 Date [MJD-52400]

0 Relativistic hadrons in leptonic jets • Naturally expected in any realistic particle acceleration scenario • For standard hadronic models: gp,max ~ 108 required (gp pion production on co-moving synchrotron photons) to work (gp*Eph > 300 MeV) • But: gp pion production on external photons possible for much lower proton Lorentz factors (gp ~ 103 – 104) → Synchrotron mirror model for pg pion production

0 The Hadronic Synchrotron Mirror Model Constraint on Rm from time delay: Rm ~ 3 G12Dt20 pc tm = 0.1 t-1 G = 10 G1 Dt = 20 Dt20 d

0 The Hadronic Synchrotron Mirror Model Estimate of reflected synchrotron photon density from Rm and observed primary synchrotron flare u’sy ~ 6.0x10-3G1-4 R16-2 ergs cm-3 Reflected sy. photons are virtually invisible to ultrarel. electrons (Klein-Nishina) Dominant contribution to pg pion production from protons with gp ~ 3,000 G1-1 Esy,1-1 • Normalization of p0 decay flare to observed secondary TeV flare • Constraint on co-moving relativistic proton density: n’p ~ 1.8x107G1-3 Esy,1Dr17t-1-1 R16-2 cm-3 Esy ~ 10 keV

0 The Hadronic Synchrotron Mirror Model Kinetic luminosity in relativistic protons in the jet: Lkinp ~ 1.8x1048 Esy,1 R16-2Dr17t-1-1 f-3 ergs/s Optical – soft X-ray synchrotron flare from p+ decay products: Dm ~ 0.05 mag Neutrino emission from charged pion decay unlikely to be detectable with current detectors (Reimer et al. 2005)

0 Some New Observational Results: 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

The Multiwavelength Campaign on 3C279 in Jan./Feb. 2006 0 • 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.

The Multiwavelength Campaign on 3C279 in Jan./Feb. 2006 0 • 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 …

0 Summary Blazar SEDs successfully be modelled with both leptonic and hadronic jet models. Blazar Sequence is NOT a prediction of either type of models. Possible multi-GeV - TeV detections of LBLs or FSRQs and spectral variability may serve as diagnostics to distinguish between models. Even in leptonically dominated models, relativistic hadrons might be present One possible diagnostic for relativistic hadrons: Orphan TeV flares without simultaneous synchrotron flare.

Spectral Variability Signatures g2 = 2*104→ 4*104 q = 2.5 → 2.3 Linj,e = 2.5*1040 erg/s → 3.5*1040 erg/s g2 = 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 g1 = 1100 g2 = 6*104 q = 2.15 D = 18 eB = 0.5 B = 1.4 G RB = 2.5*1015 cm Linj = 3*1040 erg/s g2 = 2.3*104 q = 2.4 D = 16

Modeling the Emission Processes in Blazars