Modeling the Spectral Energy Distributions and Variability of BL Lacertae in 2000

Model Constraints from Multiwavelength Variability of BlazarsMarkus BttcherNorth-West UniversityPotchefstroomSouth Africa0

BlazarsClass of AGN consisting of BL Lac objects and gamma-ray bright quasars Rapidly (often intra-day) variable0

0Blazar Variability: Example: The Quasar 3C279X-raysOpticalRadio(Bttcher et al. 2007)0Blazar Variability: Variability of PKS 2155-304

(Costamante et al. 2008)

VHE g-raysX-raysOpticalVHE g-rays(Aharonian et al. 2007)VHE g-ray and X-ray variability often closely correlatedVHE g-ray variability on time scales as short as a few minutes! See D. Dorner's and S. Ciprini's, and V. Karamanavis' Talks

Polarization Angle Swings

Optical + g-ray variability of LSP blazars often correlatedSometimes O/g flares correlated with increase in optical polarization and multiple rotations of the polarization angle (PA)PKS 1510-089 (Marscher et al. 2010)g-rays (Fermi)Optical

BlazarsClass of AGN consisting of BL Lac objects and gamma-ray bright quasars Rapidly (often intra-day) variable0Strong gamma-ray sources

Blazar Spectral Energy Distributions (SEDs)Non-thermal spectra with two broad bumps: Low-energy (probably synchrotron): radio-IR-optical(-UV-X-rays) High-energy (X-ray g-rays)3C66ACollmar et al. (2010)

BlazarsClass of AGN consisting of BL Lac objects and gamma-ray bright quasars Rapidly (often intra-day) variable0Strong gamma-ray sourcesRadio and optical polarizationRadio jets, often with superluminal motionSuperluminal Motion(The MOJAVE Collaboration)

Leptonic Blazar Model

Relativistic jet outflow with G 10Injection, acceleration of ultrarelativistic electronsQe (g,t)gSynchrotron emissionnFnnCompton emissionnFnng2g1g-qRadiative cooling escape =>0Seed photons:Synchrotron (within same region [SSC] or slower/faster earlier/later emission regions [decel. jet]), Accr. Disk, BLR, dust torus (EC) Qe (g,t)gg2g1g-(q+1)gbg-q or g-2g2gbg1gb: tcool(gb) = tesc P. Mimica's Talk

Sources of External Photons ( Location of the Blazar Zone)Direct accretion disk emission (Dermer et al. 1992, Dermer & Schlickeiser 1994) d < few 100 1000 RsOptical-UV Emission from the BLR (Sikora et al. 1994) d < ~ pcInfrared Radiation from the Obscuring Torus (Blazejowski et al. 2000) d ~ 1 10s of pc0Synchrotron emission from slower/faster regions of the jet (Georganopoulos & Kazanas 2003) d ~ pc - kpcSpine Sheath Interaction (Ghisellini & Tavecchio 2008) d ~ pc - kpc M. Georganopoulos' talk11Hadronic Blazar Models

Relativistic jet outflow with G 10Injection, acceleration of ultrarelativistic electrons and protonsQe,p (g,t)gSynchrotron emission of primary e-nFnnProton-induced radiation mechanisms:nFnng2g1g-q0 Proton synchrotron pg pp0 p0 2g pg np+ ; p+ m+nm m+ e+nenm secondary m-, e-synchrotron Cascades (Mannheim & Biermann 1992; Aharonian 2000; Mcke et al. 2000; Mcke et al. 2003)

Leptonic and Hadronic Model Fits along the Blazar SequenceRed = LeptonicGreen = HadronicSynchrotronSynchrotron self-Compton (SSC)Accretion DiskExternal Compton of direct accretion disk photons (ECD)External Compton of emission from BLR clouds (ECC)(Bttcher, Reimer et al. 2013)Electron synchrotronAccretion DiskProton synchrotron

Leptonic and Hadronic Model Fits Along the Blazar SequenceRed = leptonicGreen = lepto-hadronic3C66A (IBL)

Lepto-Hadronic Model Fits Along the Blazar SequenceRed = leptonicGreen = lepto-hadronic(HBL)In many cases, leptonic and hadronic models can produce equally good fits to the SEDs.Possible Diagnostics to distinguish:

Neutrinos Variability X-ray/g-ray Polarization

Distinguishing Diagnostic: VariabilityTime-dependent leptonic one-zone models produce correlated synchrotron + gamma-ray variability (Mastichiadis & Kirk 1997, Li & Kusunose 2000, Bttcher & Chiang 2002, Moderski et al. 2003, Diltz & Bttcher 2014)Time-dependent leptonic one-zone model for Mrk 421

See also M. Zacharias' Talk Time Lags Energy-Dependent Cooling Times Magnetic-Field Estimate!Correlated Multiwavelength Variability in Leptonic One-Zone ModelsExample: Variability from short-term increase in 2nd-order-Fermi acceleration efficiency

X-rays anti-correlated with radio, optical, g-rays; delayed by ~ few hours.(Diltz & Bttcher, 2014, JHEAp)Distinguishing Diagnostic: Variability

Time-dependent hadronic models can produce uncorrelated variability / orphan flares (Dimitrakoudis et al. 2012, Mastichiadis et al. 2013, Weidinger & Spanier 2013)(M. Weidinger)

Inhomogeneous Jet ModelsInternal Shocks (see next slides)

Radially stratified jets (spine-sheath model, Ghisellini et al. 2005, Ghisellini & Tavecchio 2008)

Decelerating Jet Model (Georganopoulos & Kazanas 2003)

Mini-jets-in-jet (magnetic reconnection D. Giannios' Talk)

The Internal Shock ModelCentral engine ejects two plasmoids (a,b) into the jet with different, relativistic speeds (Lorentz factors Gb >> Ga)GbGaGfGrShock acceleration Injection of particles with Q(g) = Q0 g-q for g1 < g < g2Sokolov et al. (2004), Mimica et al. (2004), Sokolov & Marscher (2005), Graff et al. (2008), Bttcher & Dermer (2010), Joshi & Bttcher (2011), Chen et al. (2011, 2012)Time-dependent, inhomogeneous radiation transfer Synchrotron SSC ( Light travel time effects!) External Compton(Chen et al. 2012) X. Chen's TalkInternal Shock ModelParameters / SED characteristics typical of FSRQs or LBLs

(Bttcher & Dermer 2010)

Internal Shock ModelDiscrete Correlation FunctionsX-rays lag behind HE g-rays by ~ 1.5 hrOptical leads HE g-rays by ~ 1 hrOptical leads X-rays by ~ 2 hr(Bttcher & Dermer 2010)

Parameter StudyVarying the External Radiation Energy DensityDCFs / Time LagsReversal of time lags!(Bttcher & Dermer 2010)

Polarization Angle Swings

Optical + g-ray variability of LSP blazars often correlatedSometimes O/g flares correlated with increase in optical polarization and multiple rotations of the polarization angle (PA)PKS 1510-089 (Marscher et al. 2010)Polarization Swings

3C279 (Abdo et al. 2009)Previously Proposed Interpretations:Helical magnetic fields in a bent jetHelical streamlines, guided by a helical magnetic fieldTurbulent Extreme Multi-Zone Model (Marscher 2014)

Mach diskLooking at the jet from the side

Tracing Synchrotron Polarization in the Internal Shock Model

Viewing direction in obs. Frame: qobs ~ 1/GViewing direction in comoving frame:qobs ~ p/2B

Light Travel Time EffectsShock positions at equal photon-arrival times at the observerBBBShock propagation(Zhang et al. 2014)

Flaring Scenario: Magnetic-Field Compression perpendicular to shock normalBaseline parameters based on SED and light curve fit to PKS 1510-089 (Chen et al. 2012)

Flaring Scenario: Magnetic-Field Compression perpendicular to shock normalPKS 1510-089 Synchrotron + Accretion Disk SEDsFrequency-dependent Degree of Polarization PDegree of Polarization P vs. timePolarization angle vs. time(Zhang et al. 2014)

Flaring Scenario: Magnetic-Field Compression perpendicular to shock normalMrk 421Synchrotron + Accretion Disk SEDsFrequency-dependent Degree of Polarization PDegree of Polarization P vs. timePolarization angle vs. time(Zhang et al. 2014)

SummaryBoth leptonic and hadronic models can generally fit blazar SEDs well.

Distinguishing diagnostics: Variability, Polarization, Neutrinos?

Time-dependent hadronic models are able to predict uncorrelated synchrotron vs. gamma-ray variability

Synchrotron polarization swings (correlated with g-ray flares) do not require non-axisymmetric jet features!00

Superluminal MotionApparent motion at up to ~ 40 times the speed of light!

Requirements for lepto-hadronic modelsTo exceed p-g pion production threshold on interactions with synchrotron (optical) photons: Ep > 7x1016 E-1ph,eV eV For proton synchrotron emission at multi-GeV energies: Ep up to ~ 1019 eV (=> UHECR)Require Larmor radius rL ~ 3x1016 E19/BG cm a few x 1015 cm => B 10 G(Also: to suppress leptonic SSC component below synchrotron)

=> Synchrotron cooling time: tsy (p) ~ several days=> Difficult to explain intra-day (sub-hour) variability! Geometrical effects?

Spectral modeling results along the Blazar Sequence: Leptonic ModelsHigh-frequency peaked BL Lac (HBL):

No dense circum-nuclear material No strong external photon fieldSynchrotronSSC0Low magnetic fields (~ 0.1 G);High electron energies (up to TeV);Large bulk Lorentz factors (G > 10)The classical picture(Acciari et al. 2010)

Spectral modeling results along the Blazar Sequence: Leptonic Models

FSRQPlenty of circum-nuclear material Strong external photon fieldSynchrotronExternal Compton0High magnetic fields (~ a few G);Lower electron energies (up to GeV);Lower bulk Lorentz factors (G ~ 10)

Spectral modeling with pure SSC would require extreme parameters(far sub-equipartition B-field)3C66A October 2008Intermediate BL Lac Objects

Including External-Compton on an IR radiation field allows formore natural parameters and near-equipartition B-fields(Abdo et al. 2011)(Acciari et al. 2009) g-ray production on > pc scales?38

Leptonic and Hadronic Model Fits along the Blazar SequenceRed = LeptonicGreen = HadronicSynchrotronSynchrotron self-Compton (SSC)External Compton of emission from BLR clouds (ECC)(Bttcher, Reimer et al. 2013)Electron synchrotronProton synchrotronElectron SSCProton synchrotron + Cascade synchrotronHadronic models can more easily produce VHE emission through cascade synchrotron

Diagnosing the Location of the Blazar ZoneEnergy dependence of cooling times: Distinguish between EC on IR (torus Thomson) and optical/UV lines (BLR Klein-Nishina)

(Dotson et al. 2012)

If EC(BLR) dominates:Blazar zone should be inside BLR gg absorption on BLR photons GeV spectral breaks No VHE g-rays expected!VHE g-rays from FSRQs must be from outside the BLR(e.g., Barnacka et al. 2013)(Poutanen & Stern 2010)Internal Shock Model(Chen et al. 2012)

Time-dependent SED and light curve fits to PKS 1510-089 (SSC + EC[BLR]) X. Chen's Talk