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Magnetic fields and jets as particle acceleration sites in active galaxies

Magnetic fields and jets as particle acceleration sites in active galaxies. Dr. Gizani A.B. Nectaria School of Science and Technology Hellenic Open University. Talk Outline. Acceleration of particles in AGN Jets (and containing structures, e.g. knots, hotspots)

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Magnetic fields and jets as particle acceleration sites in active galaxies

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  1. Magnetic fields and jets as particle acceleration sites in active galaxies Dr. Gizani A.B. Nectaria School of Science and Technology Hellenic Open University

  2. Talk Outline • Acceleration of particles in AGN • Jets (and containing structures, e.g. knots, hotspots) • Magnetic fields • internal (source) – polarization • external (medium) – faraday rotation • Means: Multi-λ οbservations – Interpretation • Nearby AGN • AGN and cosmic ray energy • Lessons learned from Jets and B-fields Hep 2013 Dr. Nectaria A. B. Gizani HOU

  3. AGN Terminology Chandra X-ray cavity Mathews & Guo HOST Lies in intracluster medium (ICM) Hep 2013 Dr. Nectaria A. B. Gizani HOU

  4. Acceleration in jets • Where is acceleration occurring? • location of radiating particles Multi-wavelength imaging • What kind of acceleration? • energy spectra of radiating particles Spectral energy distribution • How is acceleration occurring? • configuration of B-fields Multi-λ polarimetry • timescale of radiating population changes Multi-λ variability • How efficient is acceleration? • Energetics • Is the radiating population the majority population in jets? • Polarimetry, dynamics • e+/e-, p/e- Hep 2013 Dr. Nectaria A. B. Gizani HOU

  5. Nearby powerful AGN Jets Hep 2013 Dr. Nectaria A. B. Gizani HOU

  6. Centaurus A Low-power radio source: small-scale jet, knots: source of acceleration minimum energy) B-fields in knots and sheath ~ 10 μG knot motions@ speeds a few × 0.1c → Ekin Different knot properties→ different motions → related to nature of particle acceleration Infra-red: jet and dust Optical: too absorbed X-ray: fine-scale structure, bright core γ-ray: to Eγ > 100 GeV UHECR: > 1018 eV Combi & Romero (1997) Hep 2013 Dr. Nectaria A. B. Gizani HOU

  7. X-ray map with radio overlaid Radio : synchrotron radn X-rays from jet and sheath: also synchrotron (Crostonet al.) Well-defined NE jet in radio + X-ray Bright inner lobes, bounded by X-ray sheath to SW X-ray/radio offsets → multiple particle acceleration sites Emission loss times ~ 105 years for radio-emitting electrons, ~ 10 years for X-ray emitters. Therefore extensive local acceleration @ bright knots + diffuse region, to γ > 107 (TeV energies) in nT-scale B Worrall et al. (2008) Kraft et al. (2003) Hep 2013 Dr. Nectaria A. B. Gizani HOU

  8. 100 GeV γ-rays from centre and lobes (Fermi). TeV γ-rays from core/inner jet or lobes (HESS). IC from electrons with γ ~ 104 in lobes (B ~ 0.1 nT= μG) γ rays: SSC from core? Highest required γ ~ 108 Aharonian et al. 2010 Abdo et al. 2010 Hep 2013 Dr. Nectaria A. B. Gizani HOU

  9. M 87 (3C 274) Obvious radio jet/X-ray gas relationship X-rays: Non-thermal contains strong jet component Internal relativistic motions Polarization/intensity correlations → sheared flow Radio and X-ray structure: convective plumes lifting core material →slow entrainment Chandra X-ray + radio P-b overlaid, ~4” Residual read-out streak. Hep 2013 Dr. Nectaria A. B. Gizani HOU

  10. M87 Brightest X-ray peaks: Steep power-law spectra →synchrotron Break frequencies drop with distance from core Knots γmax ≥ 107 HST-1: High variability, like whole jet, over-pressured relative to adjacent X-ray medium, even at minimum energy VLA Log-scale VLA+HST Chandra Linear-scale Chandra + HST Marshall et al. (2002) Hep 2013 Dr. Nectaria A. B. Gizani HOU

  11. M 87 HST-1, VHE γ-ray, X-ray VLBI structure Harris et al. 2006 Flaring in radio, optical, X-ray, Superluminal 4c subcomponents Acceleration to γ ~ 106 Related to TeV mission? No HST-1 flare with 2008 flare in VHE gamma-rays (Acciari et al. 2008). Not compact enough for gamma rays – likely γ rays from core. Chandra image light curve 80 pc from core, optically thin, brightest region @ 0.6c Hep 2013 Dr. Nectaria A. B. Gizani HOU

  12. Hercules A MR = -23.75 optical z = 0.154 VLA total intensity distribution 18 cm, 1.4 arcsec Helical features HST/WFPC2, Baum et al. 1996 Ltot ~ 3.81037 W, Least,jet~ 1.6×1037 W P178 MHz = 2.3  1027 WHz–1sr–1 Hillas criterion Emax Ljet1/2 Baum et al. Gizani Hep 2013 Dr. Nectaria A. B. Gizani HOU

  13. Gizani & Leahy Collimation of jets Hep 2013 Dr. Nectaria A. B. Gizani HOU Hep 2013 Dr. Nectaria A. B. Gizani HOU

  14. Whole source: a@ -1.5; young jets, rings a@ -.7; older lobes a@ -1.5; faint material -2.5 £a£ -1.5 acore» -1.3, steep spectrum, optically thin Gizani & Leahy Snµna , a<0 Hep 2013 Dr. Nectaria A. B. Gizani HOU

  15. 0.5-2 keV, 32´´, 1st cont 2.94´10-10 Wm-2 sr-1 X-ray, Chandra, Nulsen et al • Lx » 3×1037 W • Lx point » 2×1036 W • b-Fit : • @ 0.74, rc@ 121 kpc, no» 104m-3 dense environment 0.5 < kT (keV) < 1, NH » 6.2×1020cm-2 0.3 − 7.5 keV , 2″ resoln Rosat PSPC + HRI , radio overlaid, Gizani & Leahy Hep 2013 Dr. Nectaria A. B. Gizani HOU

  16. Hercules A VLA B+C+D , 3.6 cm, 0.74 asec, rms ~ 11 mJy, ~ 6.0 mJy Gizani & Leahy @ 18 cm: ~41 mJy Hep 2013 Dr. Nectaria A. B. Gizani HOU

  17. 35° EVN, 18 cm, 0.018 arcsec 1- Gaussian fit rms» 3.6 ×10-4Jy/beam @ 14.6 mJy ~18.2 ×7 mas p.a. ~ 139° Tb@ 2 × 107 K New EVN observations scheduled in June @ 6 + 18 cm kpc-jets Gizani & Garrett Hep 2013 Dr. Nectaria A. B. Gizani HOU

  18. 3C310 HST/WFPC2 0.05´´ Van Breugel & Fomalont Chiaberge et al. VLA total intensity distribution Z =0.054, MR@ -23 central kpc emission ~^ radio jet axis, Bright pair, Martel et al 21cm, 4 arcsec P178 MHz~ 3.57 ´ 1025 Whz-1 Steep spectrum a ~ –1, FR1.5 linear correlation of optical flux of compact core with radio core Hep 2013 Dr. Nectaria A. B. Gizani HOU

  19. 3C310 Chandra X-ray , 0.5-5.0 keV , 8″ resolution, Kraft et al. X-ray cavity is offset ∼70 kpc to the northeast of the radio ring and the approximate center of the radio lobe Hep 2013 Dr. Nectaria A. B. Gizani HOU

  20. 4 mas Natural weighted 10 mas 20O Kpc-jets ~16.5 mJy » 17× 5 mas ~ 85o Tb~ 2.5×107 K Global VLBI, 18 cm, phase referencing 21 cm, 4 arcsec Gizani & Garrett ~ 130 mJy Gizani & Garrett Hep 2013 Dr. Nectaria A. B. Gizani HOU 7.3% VLA flux (~10 mJy), pola ~15o Pcore6 cm ~ 7.25 ×1023 WHz-1 8. ×7. mas

  21. Nearby powerful AGN B-fields Hep 2013 Dr. Nectaria A. B. Gizani HOU

  22. Internal B-field Perlman et al. (1999) M87, polarization Low polarization @ core in radio, high in optical. HST-1 polarization transverse. D-east patterns differ. Magnetic field mostly parallel to jet, except in (some) knots. Fractional polarization drops in knot peaks in optical. Shock + shear model. Owenet al. (1999) Apparent magnetic field directions. Hep 2013 Dr. Nectaria A. B. Gizani HOU

  23. Internal B-field Cont map: I-map, 6 cm, 1.4 arcsec contours separated by factors Ö2, 1st at 0.145 mJy/beam Gizani & Leahy Projected B-field follows closely edges, jets & ring-like structures in lobes Hep 2013 Dr. Nectaria A. B. Gizani HOU

  24. Depoln map DP3.66 , 1.4 ´´; Depoln started in west DP186 , 1.4´´ Gizani & Leahy DPl1l2= ml1/ml2 , where l1>l2 , m = p/I, fractional poln p: polarized intensity, I: total intensity Hep 2013 Dr. Nectaria A. B. Gizani HOU

  25. External B-field Hillas Criterion: Emax= Q β Β l = Ζe (u/c) B l radio (Faraday rotation) + X-ray data (e- density): n is the electron density found from Angle to the line of sight θ  50o extragalactic magnetic field of ICM has central typical value of 3 Bo(μG)  9, and radial dependence On tangling scales 4Do(kpc) 35 Hep 2013 Dr. Nectaria A. B. Gizani HOU

  26. East:-200 £RM(rad/m2 ) £200 West: RM exceeds ± 500 rad/m2 2-D B- f i e l d S T R U C T U R E Gizani RM = k<f>, f(r) = 0.81òr0neB×dlFaraday depth, l: line of sight Hep 2013 Dr. Nectaria A. B. Gizani HOU Points plotted if error RM < 5 rad/m2

  27. ICM confines the lobes very well Pmin<< Pth B-fields (μG) implied by Inverse Compton arguments Her A 4.3 → BIC≈ 3Bme 3C310 3.6 Hep 2013 Dr. Nectaria A. B. Gizani HOU

  28. Centralcosmicrayenergy gammaray production by πο-decay produced by protons interacting with ICM Analytical model fitting by Enßlin etal: correlation between the RGs’jet power vs luminosity at 2.7 GHz → energy input into the central region of cluster from host, similar in slope proton spectrum as in Galaxy Energy input ~ 1.7 ×1022 Wkpc-3 Injected jet may dissipate/heat gas or support ICM (B-fields) + particles Assume the scaling ratio between the thermal and CR energy densities to be αCR ~ 1 Hep 2013 Dr. Nectaria A. B. Gizani HOU

  29. Lessons from Jets Low-power jets • Electrons at spectral breaks have E  300 GeV • Knot spectra → synchrotron X-ray emitting electrons’ lifetime ~ 30 years in knots → locally-accelerated particles • Synchrotron spectra, radio to X-ray, with break in IR or optical, →TeV electron energy • Spectrum breaks by  > 0.5 → diagnostic of acceleration physics, electron diffusion, and dynamics • Similar spectra in knots and diffuse emission, but. knot offsets exist Hep 2013 Dr. Nectaria A. B. Gizani HOU Hep 2013 Dr. Nectaria A. B. Gizani HOU

  30. Radio steep spectral indices  short life time of radiating particles (cooling) + re-acceleration to some extent • High-power jets: BL Lacs - Flat Spectrum Radio Quasar cores • IC/CMB for X-rays → relativistic jet, γVLBI ~ 18, Extended jets have flat X-ray/gamma-ray spectrum as flat as radio spectrum (external inverse-Compton) • X-ray/gamma-ray → Synchrotron self-Compton emission spectral “second peak”, from compact bases of jets • Both mechanisms rely on relativistic boosting Hep 2013 Dr. Nectaria A. B. Gizani HOU Hep 2013 Dr. Nectaria A. B. Gizani HOU

  31. Jet Composition • May initially be electromagnetic, e+/e- plasma, or p/e- • Expect rapid entrainment with plasma • On large scales, [energy/momentum] affects dynamics → p/e- plasma (but only kinematics from radio VLBI) • Particle acceleration efficient to electron energies of many TeV, based on X–ray data, both in and between knots of jets • Value of γmin crucial for energy calculations, but not known • Leptonic/hadronic models to map the spectrum of AGN Hep 2013 Dr. Nectaria A. B. Gizani HOU

  32. Locations of acceleration • Relativistic radio JETS (parsec, kpc scales, esp. If collinear) • @ radio Jet knots (e.g. HST-1 in M87) • In-between radio jet knots – (a) turbulence developed by shear – (b) direct motion to/from across shear layer • @ radio Hotspots (strongest local concentration of kinetic energy). However not always X-rays at expected level→ upper limit of acceleration process not clear • Re-acceleration of particles by local compressions in/near radio jet • N.B. Efficiency of conversion of jet kinetic energy to radiation is low→ remainder of energy heats/displaces intercluster medium • X-ray cavities Hep 2013 Dr. Nectaria A. B. Gizani HOU

  33. Lessons from B-fields • Internal to source • Radio Jet collimation and acceleration is magnetically driven • Radio Knot magnetic fields usually ~ 10 nT ~ 100 μG • Strong radio polarization indicates B-field compression acceleration • More complex B-field distributionlowerpolndepoln in radio • Use polnto model radio jet flows • Circular poln in Quasars from (a) synchrotron emission itself (e-/p plasma + ordered B), (b) linear poln → circular poln, or internal Far.Rot , Circular poln composition Hep 2013 Dr. Nectaria A. B. Gizani HOU Hep 2013 Dr. Nectaria A. B. Gizani HOU

  34. B-field configurations Helical fields generally produce brightness and polarization distributions in sources which have asymmetric transverse profiles profiles are symmetrical only if: - no longitudinal component or - the jet @ 90o to l.o.s. in rest frame of emitting material  doppler boosted jet parsec-scale jets: If magnetic field initially disordered, then shock creates a field sheet When viewed from appropriate (rest-frame) angle, resulting emission is highly polarized Hep 2013 Dr. Nectaria A. B. Gizani HOU

  35. Using polarization to understand jets Linearly polarized radiation  anisotropic B-fields, Use this + special relativity to find jet geometries + velocities Hep 2013 Dr. Nectaria A. B. Gizani HOU

  36. B-field perpendicular @ edges of source  Deceleration: Slower at edges than on-axis  Boundary-layer entrainment deceleration acceleration Hep 2013 Dr. Nectaria A. B. Gizani HOU Cotton et al. ; RL et al.

  37. External to source • Fields around jets: random foreground (rotating plasma in front of emitting material) Inclination of source matters M87, Chandra Hep 2013 Dr. Nectaria A. B. Gizani HOU

  38. External to source cont • extragalactic magnetic field of ICM has central typical value of • Bo~ μG, and radial dependence • Field strength scales with plasma density • Faraday Rotn constrains component to l.o.s. If thermal+relativistic particles mixed • Ordered rotation measure  coherent field • Magnetization of the ICM is important for heat and momentum • Transport • Fields are not very dynamically important but are significant for • thermal conduction • No evidence for toroidal field confining jets on large scales Hep 2013 Dr. Nectaria A. B. Gizani HOU

  39. Thank you Hep 2013 Dr. Nectaria A. B. Gizani HOU

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  43. Hep 2013 Dr. Nectaria A. B. Gizani HOU

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