ICRR 17/9/2001 Gamma-ray emission from AGN Qinghuan Luo School of Physics, University of Sydney

ICRR 17/9/2001 Blazars EGRET sources: Most of them are AGN Diffuse  -ray background: - Unresolved blazars or - Exotic processes e.g. annihilation lines from supersymmetric particle dark matter or unstable particle relics? Third EGRET Catalog (Hartman et al 1999)

ICRR 17/9/2001 Mk421, Mk501

ICRR 17/9/2001 3C273, 3C279

ICRR 17/9/2001 Rapid variations Mk501

ICRR 17/9/2001 Overview Blazars (BL Lac, FSQ): Relativistic jets directed at a small angle to the line of sight. Intraday variability (IDV): small scales; large . Relativistic jets, contents, acceleration/deceleration. Emission mechanisms: SSC vs ERC? Emission from decelerating/accelerating jets?

ICRR 17/9/2001 High energy spectra of blazars At least two components: IR-UV (perhaps up to X-rays) and above hard X-rays High energy range is power-law,   =-∂lnL  /∂lnE≈ for EGRET blazars TeV  -rays; No evidence for  -ray absorption due to pair production

ICRR 17/9/2001 TeV  -rays from Mk421, Mk501 (Krennrich et al 1999) : Mk 501  : Mk 421

ICRR 17/9/2001 Escape of TeV  -rays Absorption of TeV  -rays via  +  e + +e -. The maximum photon energy:  ph ~D  max m e c 2 in the KN regime;  ph ~15TeV requires D ~30 for  =10 6. A large  is needed to explain IDV in  -ray emission from Mk 501 Photon number density n ph ≈F  d 2 /(c 3 t 2 var D 4 ) (Protheroe 1998)

ICRR 17/9/2001 TeV flares Mrk 501 -Intraday variability (possibly ~ hrs) requires relativistic beaming!

ICRR 17/9/2001 Radio IDV (Kedziora-Chudczer et al. 1997) PKS

ICRR 17/9/2001 The brightness temperature problem -VLBI measurement: -Variability brightness temperature: T var = S d 2 / 2 2 t 2 var In the jet frame T’ var ~T var /D 3 Space-based VLBI survey: the highest T b =1.8  K ( ) (Lister et al 2001; Tingay et al 2001). The intrinsic brightness temperature: T’ b =T b (1+z)/D, D=[  (  b cos  )] -1 e.g. for PKS , T var = K! (Kedziora-Chudczer et al. 1997)

ICRR 17/9/2001 Constraints on T b Synchrotron self-absorption: T b ≤ m e c 2  /k B Induced scattering: -Induced Compton scattering (kT b /m e c 2 )  T ≤ 1 (e.g. Coppi, Blandford, Rees 1993; Sincell & Krolik 1994) -Induced Raman scattering and possibly other processes Inverse Compton scattering ( Kellermann & Pauliny-Toth 1969 ) -Coherent processes is not favoured Equipartition ( Readhead 1994 )

ICRR 17/9/2001 Interpretation of radio IDV Various models - Intrinsic: Coherent emission; Geometric effects (Spada et al 1998) - Extrinsic: Interstellar scintillation Relativistic bulk beaming with  >10 needed? Synchrotron radiation by protons (Kardashev 2000) Non-stationary models (Slysh 1992) IDV may be due to both intrinsic effects and scintillation.

ICRR 17/9/2001 Relativistic bulk motions Rapid variability, high brightness temperature require relativistic bulk motion with a higher . Continuous jets or blobs? Observations of  -ray flares, IDV appear to suggest the source region being close to the central region. Both acceleration and deceleration of the jet can occur in the central region. VLBI observations:  ≤ 10. The limit of VLBI or acceleration mechanisms or radiation drag (e.g. Phinney 1987)?

ICRR 17/9/2001 Superluminal motions - Measured  obs gives only the minimum . -D from beaming models: S obs =S 0 D p (e.g. Kollgaard et al 1996) RBLs E=log(P c /P ex )

ICRR 17/9/2001 Formation of jets Radiation drag: - Radiation fields from the disk and jet’s surroundings decelerate the jet Acceleration mechanisms: no widely accepted model. - Acc. by tangled magnetic fields: Heinz & Begelman (2000) - “Twin exhaust’’ model: Blandford & Rees (1974) - Radiation acc.: O’Dell (1981) Phinney (1982, 1987):  ~  eq < 10. Sikora et al. (1996) - The unipolar model: Blandford & Znajek (1977), Macdonald & Thorne (1982)

ICRR 17/9/2001 Emission mechanisms: SSC vs ERC Synchrotron self-Compton (SSC): External radiation Compton (ERC): (e.g. Konigl 1981; Marscher & Gear 1985; Ghisellini & Maraschi 1989) Synchrotron photons are both produced and Comptonized by the same Population of electrons. The seed photons are from external sources such as disks, BR, turi, etc. (e.g. Begelman & Sikora 1987; Melia & Konigl 1989; Dermer et al. 1992) Both SSC and ERC operate

ICRR 17/9/2001 ERC Photon energy:  s ~2  2  2  (Thomson scattering)  s ~  m e c 2 (KN scattering) Luminosity: L IC =(4/  2 ) ∫ A j dr  dE e /dt  n e

ICRR 17/9/2001 Radiation drag by external photon fields

ICRR 17/9/2001 Compton drag Incoming photons Lab frame  e+e+ e-e- Jet frame Incoming photons e-e- e+e+

ICRR 17/9/2001 Compton drag (cont’d)

ICRR 17/9/2001 The KN effect

ICRR 17/9/2001 Equilibrium bulk   <  eq : radiation forces  accelerate a jet  >  eq : radiation forces  decelerate a jet When acceleration is dominant,  is determined by acceleration

ICRR 17/9/2001 Photon fields from a disk

ICRR 17/9/2001 Electron-proton jets

ICRR 17/9/2001 Extended disks Drag due to radiation fields from an extended disk - A plasma blob at z=100R g, 10 2 R g and 3  10 3 R g with  =100. Pairs have a power-law, isotropic distribution in the jet frame. -An extended disk reprocesses radiation from the inner disk. -Terminal  depends on the initial distance and jet content - KN scattering important only for  >100

ICRR 17/9/2001 Dust torus Drag due to radiation fields from disk + torus - Blazars with a dusty molecular torus? - Pier & Krolik (1992) model Deceleration region extended The unified scheme, e.g. Barthel (1989)  -ray models for blazars (e.g Protheroe 1996) Strong correlation between gamma-ray and near-IR luminosities for a sample of blazars (Xie et al. 1997)

ICRR 17/9/2001 Compton drag (cont’d) Acceleration fast enough in < 0.2pc Pair plasma in the blob relativistic The terminal  f < 20 Acceleration occurs over a larger range  f > 20 possible (determined by the acc. mechanism)

ICRR 17/9/2001 Bulk Lorentz factor Terminal Lorentz factor

ICRR 17/9/2001 Emission from dragged jets (e.g. Eldar & Levinson 2000)

ICRR 17/9/2001 SED (Wagner 1999)

ICRR 17/9/2001 L IC vs L k  =L k /L B L j =L k +L B =10 46 erg s -1. L IC =(4/  2 ) ∫ A j dr  dE e /dt  n e L IC is the received power from IC:  0 =20, 50,100 L d =10 46 erg s -1 L j =10 46 erg s -1 Z 0 =10 3 R g =5.

ICRR 17/9/2001 Equapartition but a small L j <10 46 erg s -1 Or L j =10 46 erg s -1 but L B >L k Poynting flux dominated jets?

ICRR 17/9/2001 Equipartition (e.g. Ghisellini 1999) Lj=Lk+LBLj=Lk+LB L syn  n e B’ 2 L j  L syn /(  B’) 2 L B  (  B’) 2

ICRR 17/9/2001 Multifrequency observations (Wagner 1999)

ICRR 17/9/2001 Radio emission - Photosphere: the radius  self-ab <1 - Doppler boosted T b decreases  decreases - Frequency dependence of T b - T b changes with t ?

ICRR 17/9/2001 Summary Compton drag important and should be taken into account in modeling of blazars. Radiation drag limit to the bulk  in the central region up to pc (for R g =1.5  cm). The terminal  is not well defined; It depends on acc. mechanisms, jet content (protons, cold electrons). A very large  is not favoured. Emission from the drag constrains jet models; multifrequency obs of IDV provide a test. For radio IDV, when the emission region is decelerating, change in   change frequency dependence of T b.