Markus B ӧ ttcher Ohio University Athens, OH VHE Gamma-Ray Induced Pair Cascades in Blazars and Radio Galaxies

Leptonic Blazar Models 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

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)

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

 -Absorption Features? Şentürk et al., in prep. Absorption trough from Ly  expected at E abs ~ 25/(1+z) GeV. CAVEAT: Non-simultaneous data Vastly different integration times

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

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

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

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

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

General Considerations Electron/positron escape: Energy-dependent Isotropization -> High-energy spectral turnover:  defl ( IC ) =  obs  esc (  ) =  cool (  ) -> E esc ~ E s  2

Viewing Angle B = 1 mG  B = 5 o u ext = erg cm -3 R ext = cm T BB = 1000 K  = cos  obs

External Radiation Field, u ext

Magnetic Field B  ~ 60 o B = 1  G For moderate/large inclination angles, isotropization becomes very efficient!

U ext = 5* erg/cm -3 R ext = cm B= 1 mG,     30 0 <   D = 74 MpcL BLR = 1.6x10 42 erg/s  ≈ 30 o – 55 o L BLR = 4  R 2 ext c u ext Incident (forward)  -ray spectrum normalized to a moderately bright Fermi blazar Application to NGC 1275 (Roustazadeh & B ӧ ttcher 2010)

D = 3.7 Mpc Viewing angle ~ 50 o – 80 o T = 2300 K → peak frequency at K-band Fit to the broad-band SED (Boettcher & Chiang 2002) Cascade Emission Sum of both contributions U ext = 1.5* erg/cm -3 R ext =3* cm B= 1 mG,     67 0 <   L BLR = 4  R 2 ext c u ext    ergs -1 L ~ 6X10 41 erg/s R ~ 6x10 17 cm Leptonic fit by Abdo et al. (2010) required  max = 10 8 ! Application to Cen A (Roustazadeh & B ӧ ttcher 2011)

1- Leptonic models prefer external-Compton over SSC in non- HBL blazars -> VHE  -ray emission in intense external radiation fields ->  absorption (detectable by Fermi+CTA)-> Compton supported pair cascades. 2 - VHE gamma-ray induced cascades are effectively isotropized even in weak perpendicular (B y ) magnetic fields (B y ~  G) -> 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. Summary

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

TeV  -Ray Blazars NameClasszDate Mrk421HBL /1992 Mrk501HBL /1996 1ES HBL /1998 Mrk 180HBL /2006 1ES HBL /1999 AP LibLBL /2010 PKS HBL /2007 BL LacertaeLBL /2005 PKS HBL /2005 RGBJ HBL0.0802/2008 SHBL J …HBL /2010 W ComaeIBL /2008 1ES HBL /2010 PKS HBL /1999 RGB J HBL /2009 1H HBL /2002 1ES LBL0.1301/2011 NameClasszDate 1ES HBL /2008 1ES HBL0.1402/2006 1RXS J …HBL /2010 1H HBL /2006 1ES HBL /2006 1ES HBL /2006 1ES HBL /2007 RBS 0413HBL0.1910/2009 PKS HBL0.2012/2009 1ES HBL /2007 1ES HBL /2009 S LBL /2008 1ES HBL /2009 PG HBL0.3503/2006 PKS FSRQ0.3603/2010 4C+21.35FSRQ /2010 3C66AIBL0.444 ?03/2008 3C279FSRQ /2008 PKS IBL???06/2009