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

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 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)

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)

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

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!

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 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 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 …

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

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

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.)

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.)

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

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

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

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!

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.

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