Leptonic and Hadronic Modeling of Gamma-Ray Blazars Markus Böttcher and Anita Reimer North-West University Universit ӓ t Innsbruck Potchefstroom, Innsbruck South AfricaAustria

Leptonic Blazar Model Relativistic jet outflow with  ≈ 10 Injection, acceleration of ultrarelativistic electrons Q e ( ,t)  Synchrotron emission F Compton emission F    -q Radiative cooling ↔ escape => Seed photons: Synchrotron (within same region [SSC] or slower/faster earlier/later emission regions [decel. jet]), Accr. Disk, BLR, dust torus (EC) Q e ( ,t)     -(q+1) bb  -q or  -2  bb 11  b :  cool (  b ) =  esc EBL Absorption: Finke et al. (2010)

Hadronic Blazar Model Relativistic jet outflow with  ≈ 10 Injection, acceleration of ultrarelativistic electrons and protons Q e,p ( ,t)  Synchrotron emission of primary e - F Proton- induced radiation mechanisms: F    -q Proton synchrotron p  → p  0  0 → 2  p  → n  + ;  + →  +     → e + e  → secondary  -, e-synchrotron Cascades … Radiative + adiabatic cooling Q e ( ,t)   -(q+1)  -q

Requirements for hadronic models To exceed p-  pion production threshold on interactions with synchrotron (optical) photons: E p > 7x10 16 E -1 ph,eV eV For proton synchrotron emission at multi-GeV energies: E p up to ~ eV (=> UHECR) Require Larmor radius r L ~ 3x10 16 E 19 /B G cm ≤ a few x cm => B ≥ 10 G (Also: to suppress leptonic SSC component below synchrotron)

Semi-analytical hadronic model Primary e - synchrotron + SSC as for leptonic model Power-law injection spectrum of ultrarelativistic protons Proton spectrum: Quasi-equilibrium - injection; sy., p , adiabatic cooling; Production rates of final decay products (electrons, positrons, neutrinos,  0 -decay photons) from Kelner & Aharonian (2008) templates Semi-analytical representation of cascades: -  pair production through delta-function approximation - synchrotron emissivity from single electron through j  ~ 1/3 e -     ӧ ttcher, Reimer, et al. 2013)

X-Ray and Gamma-Ray Polarization Synchrotron polarization: Standard Rybicki & Lightman description SSC Polarization: Bonometto & Saggion (1974) for Compton scattering in Thomson regime For both leptonic and hadronic models: Upper limits on high-energy polarization, assuming perfectly ordered magnetic field perpendicular to the line of sight (Zhang & B ӧ ttcher, 2013, ApJ, submitted)

Comparative Modeling of Gamma-Ray Blazars with Leptonic and Hadronic Models 6 FSRQs 4 LBLs 2 IBLs

Leptonic and Hadronic Model Fits to FSRQs Red = Leptonic Green = Hadronic Synchrotron Synchrotron self- Compton (SSC) Accretion Disk External Compton of direct accretion disk photons (ECD) External Compton of emission from BLR clouds (ECC) (B ӧ ttcher, Reimer et al. 2013) Electron synchrotron Accretion Disk Proton synchrotron

Polarization: 3C454.3 Hadronic model: Synchrotron dominated => High  Leptonic model: X-rays SSC dominated:  ~ 20 %;  -rays EC dominated => Negligible . (Zhang & B ӧ ttcher 2013)

Leptonic and Hadronic Model Fits to LBLs Red = Leptonic Green = Hadronic Synchrotron Synchrotron self- Compton (SSC) External Compton of emission from BLR clouds (ECC) (B ӧ ttcher, Reimer et al. 2013) Electron synchrotron Proton synchrotron Electron SSC Proton synchrotron + Cascade synchrotron Hadronic models can more easily produce VHE emission through cascade synchrotron

Polarization: BL Lacertae Hadronic model: Mostly synchrotron dominated => High  except for X-rays, where SSC may dominate. Leptonic model: X-rays = transition from sy. to SSC:  rapidly decreasing with energy;  -rays EC dominated => Negligible . (Zhang & B ӧ ttcher 2013)

Leptonic and Hadronic Model Fits to IBLs Red = Leptonic Green = Hadronic Synchrotron Synchrotron self- Compton (SSC) External Compton of emission from warm dust (ECIR) (B ӧ ttcher, Reimer et al. 2013) Electron synchrotron Proton synchrotron Electron SSC Proton synchrotron + Cascade synchrotron Both models have problems with apparent upturn at HE gamma-rays

Polarization: 3C66A Hadronic model: Synchrotron dominated => High  throughout X-rays and  -rays Leptonic model: X-rays sy. Dominated => High  rapidly decreasing with energy;  -rays SSC/EC dominated => Small . (Zhang & B ӧ ttcher 2013)

Characteristic Model Parameters ParameterLeptonic model Hadronic model Kinetic jet power in electrons L e [erg/s](5 – 10) x (1 – 10) x Kinetic jet power in protons L p [erg/s] (n p = n e )(5 – 90) x (3 – 40) x Magnetic field [G]1 – 410 – 20 Doppler factor D15 – 25 Electron injection  min ~ – 900 Electron injection  max ~ 5 x 10 4 (1 – 4) x 10 4 Electron injection index q e 3.2 – – 4.1 Proton injection  max [eV] (1 - 4) x Proton injection index q p 1.6 – 2.4 Flat Spectrum Radio Quasars (FSRQs) Strongly proton dominated Proton dominated (if n e ~ n p ), approx. e-B equipartition

Characteristic Model Parameters ParameterLeptonic model Hadronic model Kinetic jet power in electrons L e [erg/s](1 – 10) x ( ) x Kinetic jet power in protons L p [erg/s] (n p = n e )(5 – 90) x ~10 49 Magnetic field [G]1 – 310 – 100 Doppler factor D10 – 20 Electron injection  min ~ – 300 Electron injection  max ~ 10 5 ~ 10 4 Electron injection index q e 3.0 – 3.5 Proton injection  max [eV] (5 – 50) x Proton injection index q p 1.3 – 2.4 Low-Frequency-Peaked BL Lacs (LBLs) Strongly proton dominated Proton dominated (if n e ~ n p ), approx. e-B equipartition

Characteristic Model Parameters ParameterLeptonic model Hadronic model Kinetic jet power in electrons L e [erg/s](1 – 10) x (1 - 30) x Kinetic jet power in protons L p [erg/s] (n p = n e )(1 – 10) x ~(2 – 100) x Magnetic field [G]0.1 – 110 – 30 Doppler factor D – 30 Electron injection  min ~ (1 – 9) x 10 3 ~ 800 Electron injection  max ~ 10 5 ~ (1 – 2) x 10 4 Electron injection index q e 2.4 – – 2.8 Proton injection  max [eV] ~ 1.5 x Proton injection index q p 2.0 Intermediate BL Lacs (IBLs) Strongly proton dominated Approx. Equipartition between all constituents

Summary Both leptonic and hadronic origin of high-energy emission from AGN jets are viable. Leptonic models often possible near (e - - B) equipartition (but proton dominated if n p = n e ); hadronic models always proton dominated. Hadronic models consistent with AGN jets as sources of UHECRs; require large jet powers (10 47 – erg/s). Possible distinguishing diagnostics: (1) Rapid, (un)-correlated variability (2) X-ray (gamma-ray?) polarization Based on: B ӧ ttcher, M., Reimer, A., Sweeney K., & Prakash, A., 2013, ApJ, 768, 54 Zhang, H. & B ӧ ttcher, M., 2013, ApJ, submitted

A Word from the Shameless- Commerce Department

Spectral modeling results along the Blazar Sequence: Leptonic Models High-frequency peaked BL Lac (HBL): No dense circumnuclear material → No strong external photon field Synchrotron SSC Low B fields (~ 0.1 G); High electron energies (up to TeV); Large bulk Lorentz factors (  > 10) The “classical” picture

Spectral modeling results along the Blazar Sequence: Leptonic Models Radio Quasar (FSRQ) Plenty of circumnuclear material → Strong external photon field Synchrotron External Compton High magnetic fields (~ a few G); Lower electron energies (up to GeV); Lower bulk Lorentz factors (  ~ 10)

Problems of spherical, homogeneous, leptonic models Apparently uncorrelated variability among optical / X-rays /  -rays 1ES (2002) PKS ( ) (Marscher al. 2010) (Krawczynski et al. 2004)

Models already used for several VERITAS blazars… 1ES ES C66A RXJ 0648

Caveats (Hadronic model) Neglecting  synchrotron radiation => Need (a) proton energy losses synchrotron dominated or(b) t decay,  << t sy,   B << 56 /  p,9 G Neglecting external radiation fields But may be important in FSRQs (depending on R BLR and location of emission region)

Leptonic and Hadronic Model Fits to FSRQs Red = Leptonic Green = Hadronic Synchrotron Synchrotron self- Compton (SSC) Accretion Disk External Compton of direct accretion disk photons (ECD) External Compton of emission from BLR clouds (ECC) (B ӧ ttcher, Reimer et al. 2013) Electron synchrotron Accretion Disk Proton synchrotron Hadronic model: Problems with Fermi spectral index and spectral breaks.

Leptonic and Hadronic Model Fits to LBLs Red = Leptonic Green = Hadronic Synchrotron Synchrotron self- Compton (SSC) External Compton of direct accretion disk photons (ECD) External Compton of emission from BLR clouds (ECC) (B ӧ ttcher, Reimer et al. 2013) Electron synchrotron Proton synchrotron Electron SSC Leptonic model: Problems with mismatch between synchrotron and gamma-ray spectral indices