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Markus B ӧ ttcher Ohio University Athens, OH

VHE Gamma-Ray Induced Pair Cascades in Blazars and Radio Galaxies. Markus B ӧ ttcher Ohio University Athens, OH. 0. Leptonic Blazar Models. Synchrotron emission. Injection, acceleration of ultrarelativistic electrons. Relativistic jet outflow with G ≈ 10. n F n. g -q. Q e ( g ,t).

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Markus B ӧ ttcher Ohio University Athens, OH

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  1. VHE Gamma-Ray Induced Pair Cascades in Blazars and Radio Galaxies Markus Bӧttcher Ohio University Athens, OH

  2. 0 LeptonicBlazarModels Synchrotron emission Injection, acceleration of ultrarelativistic electrons Relativistic jet outflow with G≈ 10 nFn g-q Qe (g,t) n Compton emission g1 g2 g Radiative cooling ↔ escape => nFn 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 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

  4. 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 Synchrotron Plenty of circumnuclear material → Strong external photon field

  5. Intermediate BL Lac Objects 3C66A October 2008 (Abdo et al. 2011) (Acciari et al. 2009) Spectral modeling with pure SSC would require extreme parameters (far sub-equipartition B-field) Including External-Compton on an IR radiation field allows for more natural parameters and near-equipartition B-fields

  6. gg-Absorption Features? • CAVEAT: • Non-simultaneous data • Vastly different integration times Absorption trough from Lya expected at Eabs~ 25/(1+z) GeV. Şentürk et al., in prep.

  7. gg-Absorption Features? M. Errando - Şentürk et al., in prep.

  8. gg-Absorption Features? M. Errando - Şentürk et al., in prep.

  9. VHE Gamma-Ray Induced Pair Cascades VHE g-ray production within dense external radiation fields • gg absorption • Pair cascades • Deflection by B-fields HE g-ray Detections of Radio Galaxies: M 87 , NGC 1275, 3C 120, 3C 270, 3C 380 3C 111, NGC 6251, Cen A Fermi EGRET + Fermi

  10. Model Setup Arbitrary ext. photon spectrum Monoenergetic optical/UV (BLR) Thermal IR (torus) Power-law spectrum of HE – VHE g-rays from the inner jet The trajectories of the particles are followed in full three-dimensional geometry.

  11. Compton vs. Synchrotron Inverse Compton Scattering dominates In AGN env.: Compton supported cascades Deflection, isotropization

  12. General Considerations • Energy-dependent Isotropization • -> High-energy spectral turnover: • qdefl(lIC) = qobs • Electron/positron escape: tesc(g) = tcool(g) -> Eesc ~ Esg2

  13. Viewing Angle B = 1 mG qB = 5o uext = 10-5 erg cm-3 Rext = 1018 cm TBB = 1000 K • = cosqobs

  14. External Radiation Field, uext

  15. Magnetic Field B q ~ 60o B = 1 mG For moderate/large inclination angles, isotropization becomes very efficient!

  16. Application to NGC 1275 D = 74 Mpc LBLR = 1.6x1042 erg/s q≈ 30o – 55o Incident (forward) g-ray spectrum normalized to a moderately bright Fermi blazar U ext = 5* 10 -2 erg/cm -3 R ext = 10 16 cm B= 1 mG, q B = 80 L BLR = 4 p R2ext c uext 300 < q < 430 (Roustazadeh & Bӧttcher 2010)

  17. Application to Cen A D = 3.7 Mpc Viewing angle ~ 50o – 80o nLn ~ 6X1041 erg/s R ~ 6x1017 cm Leptonic fit by Abdo et al. (2010) required gmax = 108! Sum of both contributions T = 2300 K → peak frequency at K-band U ext = 1.5* 10 -3 erg/cm -3 R ext =3* 10 16 cm B= 1 mG, q B = 40 L BLR = 4 p R2ext c uext = 5*1041ergs-1 670 < q < 730 (Roustazadeh & Bӧttcher 2011) Fit to the broad-band SED (Boettcher & Chiang 2002) Cascade Emission

  18. Summary 1- Leptonic models prefer external-Compton over SSC in non-HBL blazars -> VHE g-ray emission in intense external radiation fields -> gg absorption (detectable by Fermi+CTA)-> Compton supported pair cascades. 2- VHE gamma-ray induced cascades are effectively isotropized even in weak perpendicular (By) magnetic fields (By ~ mG) -> MeV- GeV gamma-ray flux in directions misaligned with respect to the jet axis. 3- Fermi detections of radio galaxies (NGC 1275, Cen A) can be modeled as off-axis VHE gamma-ray induced pair cascade emission.

  19. 0 Blazar Classification 3C66A (Abdoet al. 2011) (Acciariet al. 2009) (Hartman et al. 2000) Low-frequency peaked / Intermediate BL Lacs (LBLs/IBLs): Peak frequencies at IR/Optical and GeVgamma-rays, 1014 Hz < nsy ≤ 1015 Hz Intermediate overall luminosity Sometimes g-ray dominated High-frequency peaked BL Lacs (HBLs): Low-frequency component from radio to UV/X-rays, nsy > 1015 Hz often dominating the total power High-frequency component from hard X-rays to high-energy gamma-rays Quasars: Low-frequency component from radio to optical/UV, nsy ≤ 1014 Hz High-frequency component from X-rays to g-rays, often dominating total power

  20. TeVg-Ray Blazars

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