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Leptonic and Hadronic Modeling of Gamma-Ray Blazars

0. Leptonic and Hadronic Modeling of Gamma-Ray Blazars. Markus B öttcher and Anita Reimer North-West University Universit ӓ t Innsbruck Potchefstroom, Innsbruck South Africa Austria. 0. Leptonic Blazar Model. Synchrotron emission. Relativistic jet outflow with G ≈ 10.

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Leptonic and Hadronic Modeling of Gamma-Ray Blazars

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  1. 0 Leptonic and Hadronic Modeling of Gamma-Ray Blazars Markus Böttcher and Anita Reimer North-West University Universitӓt Innsbruck Potchefstroom, Innsbruck South Africa Austria

  2. 0 Leptonic Blazar Model Synchrotron emission Relativistic jet outflow with G≈ 10 Injection, acceleration of ultrarelativistic electrons nFn g-q Qe (g,t) n n Compton emission g1 g2 g Radiative cooling ↔ escape => nFn EBL Absorption: Finke et al. (2010) g-q or g-2 n Qe (g,t) g-(q+1) Seed photons: Synchrotron (within same region [SSC] or slower/faster earlier/later emission regions [decel. jet]), Accr. Disk, BLR, dust torus (EC) g1 gb g2 g gb: tcool(gb) = tesc gb g1 g2

  3. 0 Hadronic Blazar Model Proton-induced radiation mechanisms: Relativistic jet outflow with G≈ 10 Injection, acceleration of ultrarelativistic electrons and protons nFn g-q Qe,p (g,t) n • Proton synchrotron g1 g2 g • pg→ pp0p0 →2g Radiative + adiabatic cooling Synchrotron emission of primary e- • pg→ np+ ; p+ → m+nm • m+→ e+nenm g-q Qe (g,t) nFn → secondary m-, e-synchrotron g-(q+1) g n • Cascades …

  4. Requirements for hadronic models • To 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)

  5. 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., pg, adiabatic cooling; • Production rates of final decay products (electrons, positrons, neutrinos, p0-decay photons) from Kelner & Aharonian (2008) templates • Semi-analytical representation of cascades: - gg pair production through delta-function approximation - synchrotron emissivity from single electron through jn (g) ~ n1/3e-n/n0(g) (Bӧttcher, Reimer, et al. 2013)

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

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

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

  9. Polarization: 3C454.3 Hadronic model: Synchrotron dominated => High P • Leptonic model: • X-rays SSC dominated: • ~ 20 %; • g-rays EC dominated • => Negligible P. (Zhang & Bӧttcher 2013)

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

  11. Polarization: BL Lacertae Hadronic model: Mostly synchrotron dominated => High P, except for X-rays, where SSC may dominate. • Leptonic model: • X-rays = transition from sy. to SSC: • rapidly decreasing with energy; • g-rays EC dominated • => Negligible P. (Zhang & Bӧttcher 2013)

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

  13. Polarization: 3C66A Hadronic model: Synchrotron dominated => High P, throughout X-rays and g-rays Leptonic model: X-rays sy. Dominated => High P, rapidly decreasing with energy; g-rays SSC/EC dominated => Small P. (Zhang & Bӧttcher 2013)

  14. Characteristic Model Parameters Flat Spectrum Radio Quasars (FSRQs) Proton dominated (if ne ~ np), approx. e-B equipartition Strongly proton dominated

  15. Characteristic Model Parameters Low-Frequency-Peaked BL Lacs (LBLs) Proton dominated (if ne ~ np), approx. e-B equipartition Strongly proton dominated

  16. Characteristic Model Parameters Intermediate BL Lacs (IBLs) Approx. Equipartition between all constituents Strongly proton dominated

  17. 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 np = ne); hadronic models always proton dominated. • Hadronic models consistent with AGN jets as sources of UHECRs; require large jet powers (1047 – 1049 erg/s). • Possible distinguishing diagnostics: (1) Rapid, (un)-correlated variability (2) X-ray (gamma-ray?) polarization Based on: Bӧttcher, M., Reimer, A., Sweeney K., & Prakash, A., 2013, ApJ, 768, 54 Zhang, H. & Bӧttcher, M., 2013, ApJ, submitted

  18. A Word from the Shameless-Commerce Department

  19. 0 Spectral modeling results along the Blazar Sequence: Leptonic Models High-frequency peaked BL Lac (HBL): Low B fields (~ 0.1 G); High electron energies (up to TeV); Large bulk Lorentz factors (G > 10) The “classical” picture No dense circumnuclear material → No strong external photon field Synchrotron SSC

  20. 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

  21. Problems of spherical, homogeneous, leptonic models Apparently uncorrelated variability among optical / X-rays / g-rays 1ES 1959+650 (2002) PKS 1510-089 (2008 - 2009) (Marscher al. 2010) (Krawczynski et al. 2004)

  22. Models already used for several VERITAS blazars… 3C66A RXJ 0648 1ES 0502 1ES 0414

  23. Caveats (Hadronic model) • Neglecting p, m synchrotron radiation => Need (a) proton energy losses synchrotron dominated or (b) tdecay,m << tsy,m B << 56 / gp,9 G • Neglecting external radiation fields But may be important in FSRQs (depending on RBLR and location of emission region)

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

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

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