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Blazars: the broad band observational point of view

Blazars: the broad band observational point of view. Annalisa Celotti S.I.S.S.A., Italy celotti@sissa.it. Blazar Variability across the Electromagnetic Spectrum Ecole Polytechnique, Palaiseau - Apr. 2008. Outline. Intro & Open questions on blazars Broad band view: what can we learn?

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Blazars: the broad band observational point of view

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  1. Blazars: the broad band observational point of view Annalisa Celotti S.I.S.S.A., Italy celotti@sissa.it Blazar Variability across the Electromagnetic SpectrumEcole Polytechnique, Palaiseau - Apr. 2008

  2. Outline • Intro & Open questions on blazars • Broad band view: what can we learn? • Sequence yes, sequence no • More than blazars Variability provides key pieces of information

  3. Intro & Open questions Active Galactic Nuclei • Inflow: energy from accretion onto SMBH accretion rate and mode ? • Outflows: jets/winds total and relative energetics ? relativistic jets – 10 % AGN are `jetted’ + Orientation effects: obscuration and/or Doppler beaming Blazars are dominated by relativistically beamed emission

  4. Intro & Open questions `Big’ questions on blazars • How do jets form ? • Magnetic processes ? • Powered by disk or BH spin? • What are they made of ? • Baryonic vs pair vs el.m. plasma? • Efficiency of energy transport ? • Power: bulk Lorenz factor vs mass loading • Dissipation: internal, recollimation shocks vs. reconnection? • Particle acceleration • How do they propagate and interact with environ ? • Gas: entrainment, boundary layers • Radiation: ambient photon fields

  5. Intro & Open questions Some issues on which observations can more directly help clarifying • Emission processes • Jet power and content • Connection accretion properties and jets • Dissipation site and mechanism • Mapping the ambient • Jet structure • Cosmic evolution • Population studies and unification models • g– ray background • IR-Optical-UV backgrounds • …

  6. Intro & Open questions pc lobes/bubbles blazar 100 kpc resolved z=0.01; 300 kpc Images courtesy of NRAOAUI Cyg A tvar 1016-17 cm

  7. Broad band we: what do we learn? Emission processes (Wehrle et al. 1998) Broadband spectra: two components (Macomb et al. 1995) Modeling of emission allows (in principle) to infer physical quantities

  8. Broad band we: what do we learn? IR-X GeV-TeV Synchrotron Simplest model: same electrons produce both peaks ? Fossati et al. 98

  9. Broad band we: what do we learn? External Compton [Sikora, Begelman & Rees 1993] G

  10. Broad band we: what do we learn? Synchrotron self-Compton + External Compton on BLR, disc, torus,… Synchrotron Fossati et al. 98 “Hadronic” models [p+p, p+B, p+g  p …]some difficulties (timescales, efficiency). Ruled out ?

  11. Broad band we: what do we learn? EC 3c273 SSC PIC von Montigny et al 98 SSC vs EC vs more complex models: How to distinguish? Broad band distribution could not discriminate so far (errors, variability) Multiwavelength correlations esp. at peaks(strong for SSC, weaker for EC) are key info • Seen especially on shorter flares, but exceptions • Limited by 1 day resolution timescale with EGRET, shorter timescales from TeV • Coverage poor in some bands (e.g. FIR) • Light curve correlations (radio/g-ray): mapping the dissipation

  12. Broad band we: what do we learn? Jet power and content Ljet > 1047 erg/s Log nLn Fabian et al. 1998 Log n But need duty cycles! Ljet> Lobs/G2

  13. Broad band we: what do we learn? Via spectral modeling B,n,…  Powers Protons (one p per emitting e-) Relat. electrons B-field Radiation Cold elecrons

  14. Broad band we: what do we learn? X-ray G UV [Begelman & Sikora 1987] Bulk Comptonization `cold’ leptons <g> ~ 1

  15. Broad band we: what do we learn? Bulk Compton bump Steepening wrt power law Flattening wrt power law ~ G2 Soft X Bulk Comptonization Logn Ln Logn UV

  16. Broad band we: what do we learn? 1428+4217 z=4.72 Yuan et al. 2005 ..or a bump ? 1028.6-0844 z=4.276 If detected get info on: # `cold’ particles, G Soft X-ray flattening due to absorption… Statistically equally consistent

  17. Broad band we: what do we learn? Accelerating jet G ~ Ra G Multicolor BB

  18. Broad band we: what do we learn? G

  19. Broad band we: what do we learn? BLR G

  20. Broad band we: what do we learn? Multicolor BB 18-21 BC of disk BC of BLR 0-3 X-rays - Transient feature - Difficult to observe (low SSC) - Powerful (i.e. high z) blazars favored

  21. Broad band we: what do we learn? Disc contribution can be important PMN J0525-3343 [Fabian et al. 2001] PKS1510-089 [Kataoka 2007] IGR J22517+2218 [Bassani et al 2007] …. Relative normalization relativistic and ‘cold’ leptons requires high energy component Delays: mapping the dissipation vs acceleration ?

  22. ~100 Rs X ~100 Rs Low entropy inner jet X-rays Log n e+e- g g-g -> e+e- UV X Log nL(n) tgg~1 Dissipation, transport of energy Dissipation site(s) Variability sets upper limit Pair opacity sets lower limit Internal shocks vs standing recollimation shock vs reconnection ? Characteristic variability timescale ? PDS Problem for models involving pair cascading (hadronic)

  23. G > G Internal shocks Unsteady velocity ‘injection’ • Typical distance for dissipation ~ R0G2 ~100 Rs, but highly variable • Low radiative efficiency • Lkin > Lel.m in contrast with el.m. model

  24. Numerical simulations for 3C 279 Spada et al 2001

  25. and Mkn 421 Overall spectrum depends on <Ljet > Large Ljet ~ FSRQ Low Ljet ~ HBL Guetta et al 2004 Variability indicators

  26. Broad band we: what do we learn? Evolution 0906+6930 z = 5.47 How many ? `Low’ z Evolution in environment ? (nuclear,host,…) Romani et al 200? GLAST tvar/(1+z) z > 4 High z blazars But EBL…

  27. Sequence yes, sequence no Lc/Lsyn L npeak A blazar sequence? phenomenological Fossati et al. 98 Fossati et al. 98

  28. Sequence yes, sequence no gpeak ~ U-1 Cooling ? Quasars - Strong ambient radiation = EC BL Lac - Weak ambient radiation = SSC IF a blazar sequence defines a disc–jet connection FSRQ Padovani et al 2002 LBL HBL Fossati et al. 98

  29. Sequence yes, sequence no GLAST Sequence or selection effects? Possibly biased: 3 samples Poor coverage high energy peak Weak-low npeak sources ? Powerful-high npeak sources ? Statistic populations Spurious physical effect

  30. Sequence yes, sequence no Selection effects vs sequence? Samples Many outliers: majority are weak red blazars Simply debeamed sources? Poorly sampled and non simultaneous SEDs SEDs of large samples Thermal disk contribution ? Surveys: broad band spectral indices EMSS? Statistics populations Requires info on LF

  31. Sequence yes, sequence no EMSS FSRQ [Wolter & Celotti 2001] EMSS BL Lacs = HBL EMSS “Significant fraction of HFLRS in DXRBS, RGB…. And up to 80% in the EMSS (weighing for exposure) “ [Padovani et al 2003]

  32. Sequence yes, sequence no Maraschi et al 2007 Selection effects vs sequence? Single sources They belong to sequence but with low luminosity broad lines) Two FLRQs with npeak ~1016 Hz They are rare None with higher npeak Selection effect: powerful HFSRQ have no visible lines  no redshift ? Powerful extended radio sources with BL Lac core ? Intermediate HBL with broad lines?

  33. Sequence yes, sequence no IGRJ22517+2218[Bassani et al. 2007] [Fabian et al 99] [Teshima et al. 2007] Selection effects vs sequence? Single sources They belong to sequence but with low luminosity broad lines) Two FLRQs with npeak ~1016 Hz They are rare None with higher npeak Selection effect: powerful HFSRQ have no visible lines  no redshift ? Powerful extended radio sources with BL Lac core ? Intermediate HBL with broad lines? Same behavior as a handful of very powerful high redshift blazars Two FLRQs with very high npeak? Or a new class? FSRQ (3C279) in TeV band But how much and where npeak?

  34. Maybe more than blazars BL Lac Jet structure Radio galaxies Emission higher than expected from simple de-beaming in FRI Mildly beamed component at larger angles? Chiaberge et al. 2000 Structured jets due to Ljet (q) or interaction with environment ?

  35. Maybe more than blazars Radiogalaxies so far only FRI - HESS: rapid TeV variability in M87 ? - Non variable reprocessed extended component

  36. 1045 erg/s Lradio BLAZARS 1041 erg/s Lopt Non blazars jetted AGN Radio intermediate quasars: `low speed’ jets?

  37. What about NON variability ? or… Is there a minimum flux level? • Faint component • `Steady’ physical process and/or large scale emission

  38. Conclusions Fundamental physical and phenomenological issues still open. CTA, GLAST & Swift hold great promises to get insights into the physics of relativistic jets (and more) via multi-wavelength coordinated programs. Variability is a necessary (and promising) tool to make progress.

  39. Thanks!

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