Post on 05-Jan-2016
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
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
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
AGN TerminologyAGN Terminology
HOSTHOST
Lies in intracluster medium (ICM)
Chandra X-rayChandra X-ray
Mathews & Guo
cavity
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
Acceleration in jetsAcceleration in jetsWhere is acceleration occurring?Where is acceleration occurring?
• location of radiating particles Multi-wavelength imaginglocation of radiating particles Multi-wavelength imaging
What kind of acceleration?What kind of acceleration?• energy spectra of radiating particles Spectral energy distributionenergy spectra of radiating particles Spectral energy distribution
How is acceleration occurring?How is acceleration occurring?• configuration of B-fields Multi-configuration of B-fields Multi-λ λ polarimetry polarimetry• timescale of radiating population changes Multi-timescale of radiating population changes Multi-λλ variability variability
How efficient is acceleration?How efficient is acceleration?• EnergeticsEnergetics
Is the radiating population the majority population in jets?Is the radiating population the majority population in jets?• Polarimetry, dynamicsPolarimetry, dynamics ee++/e/e--, p/e, p/e--
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
Centaurus ALow-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)
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
Radio : synchrotron radn X-rays Radio : synchrotron radn X-rays from jet and sheath: also from jet and sheath: also synchrotron (Croston synchrotron (Croston et alet al.).)
Well-defined NE jet in radio + X-Well-defined NE jet in radio + X-rayray
Bright inner lobes, bounded by Bright inner lobes, bounded by X-ray sheath to SWX-ray sheath to SW
X-ray/radio offsets → multiple X-ray/radio offsets → multiple particle acceleration sitesparticle acceleration sites
Emission loss times ~ 10Emission loss times ~ 1055 years years for radio-emitting electrons, for radio-emitting electrons, ~ ~ 10 10 years for X-ray emitters.years for X-ray emitters.
Therefore extensive Therefore extensive locallocal acceleration @ bright knots + acceleration @ bright knots + diffuse region, to diffuse region, to γγ > 10 > 1077 (TeV (TeV energies) in nT-scale Benergies) in nT-scale B
Kraft et al. (2003)
X-ray map with radio overlaid
Worrall et al. (2008)
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
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
Abdo et al. 2010
Aharonian et al. 2010
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
M 87 (3C 274)
Residual read-out streak.
Chandra X-ray + radio P-b overlaid, ~4”
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
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M87Brightest 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 Marshall et al. (2002)
VLALog-scale
VLA+HST
ChandraLinear-scale
Chandra +
HST
Hep 2013 Dr. Nectaria A. B. Gizani HOU
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M 87 HST-1, VHE γ-ray, X-ray
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.
Harris et al. 2006
ChandraChandra
image
light curve
VLBI structure
80 pc from core, optically thin, brightest region @ 0.6c
Hep 2013 Dr. Nectaria A. B. Gizani HOU
Hercules A
Gizani
VLA total intensity distribution 18 cm, 1.4 arcsec
Ltot ~ 3.81037 W, Least,jet~ 1.6×1037 W
P178 MHz
= 2.3 1027 WHz–1sr–1 Hillas criterion Emax Ljet1/2
z = 0.154z = 0.154
Helical features
HST/WFPC2, Baum et al. 1996
MR = -23.75 opticaloptical
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Baum et al.
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Co
llim
atio
n o
f C
olli
mat
ion
of
jets
jets
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Gizani & Leahy
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Whole source: -1.5; young jets, rings -.7; older lobes -1.5; faint material -2.5 -1.5
S<0
core
-1.3, steep spectrum, optically thin
Gizani & Leahy
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
0.3 − 7.5 keV , 2″ resoln
Lx ×W Lx
point 2×1036 W
Fit : , r
c 121 kpc,
no 104 m-3
dense environment0.5 < kT keV) < 1, N
H 6.2×cm-2
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Rosat PSPC + HRI , radio overlaid, Gizani & Leahy
0.5 - 2 keV, 32´´, 1st cont 2.94 Wm-2 sr-1 X-ray, Chandra, Nulsen et al
Hep 2013 Dr. Nectaria A. B. Gizani HOU
Hercules A
VLA B+C+D , 3.6 cm, 0.74 asec, rms ~ 11 Jy, ~ 6.0 mJy
@ 18 cm: ~41 mJy
Gizani & Leahy
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
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
35°
EVN, 18 cm, 0.018 arcsec
Gizani & Garrett17
Hep 2013 Dr. Nectaria A. B. Gizani HOU
VLA total intensity distribution Van Breugel & Fomalont
21cm, 4 arcsec
P178 MHz~ 3.57 1025 Whz-1
Steep spectrum Steep spectrum ~ ~ ––1, FR1.51, FR1.5
3C310
linear correlation of optical flux of compact core with linear correlation of optical flux of compact core with radio core radio core
HSTHST//WFPC2 0.05´´WFPC2 0.05´´
Chiaberge et al.Chiaberge et al.
Z =0.054, Z =0.054, MMRR2323
central kpc emission central kpc emission radio jet axis, radio jet axis, Bright pair, Bright pair, Martel et alMartel et al
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
Chandra X-ray , 0.5-5.0 keV , 8″ resolution, Kraft et al.
3C310
X-ray cavity is offset 70 kpc to the northeast of the radio ring and the ∼approximate center of the radio lobe
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Pcore6 cm ~ 7.25 ×1023 WHz-1
~ 130 mJy
21 cm, 4 arcsec
Hep 2013 Dr. Nectaria A. B. Gizani HOU
4 mas
20O
~16.5 mJy17× 5 mas ~ 85o
Tb 2.5×107 K
Natural weighted 10 mas
Global VLBI, 18 cm, phase referencing
Kpc-jetsGizani & Garrett
Gizani & Garrett
7.3% VLA flux (~10 mJy), pola ~15o 8. ×7. mas
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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.
Owen et al. (1999)
Apparent magnetic field directions.
Perlman et al. (1999)Internal B-field
Hep 2013 Dr. Nectaria A. B. Gizani HOU
Cont map: I-map, 6 cm, 1.4 arcseccontours separated by factors 2, 1st at 0.145 mJy/beam
Projected B-field follows closely edges, jets & ring-like structures in lobes
Gizani & Leahy
Internal B-field
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
Depoln map DP3.66 , 1.4 ´´; Depoln started in west
DPm/m, where m = p/I, fractional
poln p: polarized intensity, I: total intensity
DP186 , 1.4´´
Gizani & Leahy
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
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
1 2
2 1( ) ,o o on r n r r r r
m-1B r = B n
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External B-field
Hillas Criterion: Emax = Q β Β l = Ζe (u/c) B l
Hep 2013 Dr. Nectaria A. B. Gizani HOU
East:200 RM(rad/m2 ) 200 West: RM exceeds 500 rad/m2
RM = k<>, rr0n
eBdlFaraday depth, l: line of
sight Points plotted if error RM < 5 rad/m2
Gizani
2-DB-field
STRUCTURE
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
ICM confines the lobes very wellICM confines the lobes very well PPminmin<< P<< Pthth
B-fields (B-fields (μμG) implied by Inverse Compton argumentsG) implied by Inverse Compton arguments
Her A 4.3 Her A 4.3 → → BBICIC ≈ 3B ≈ 3Bmeme
3C310 3.63C310 3.6 27
Central cosmic ray energy gamma ray production by πο-decay produced by protons interacting with ICM
Hep 2013 Dr. Nectaria A. B. Gizani HOU
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 W kpc-3
Assume the scaling ratio between the thermal and CR energy densities to be αCR ~ 1
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Injected jet may dissipate/heat gas or support ICM (B-fields) + particles
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Lessons from JetsLessons from JetsLow-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 HOUHep 2013 Dr. Nectaria A. B. Gizani HOU
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
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Radio steep spectral indices short life time of radiating particles (cooling) + re-acceleration to some extent
Jet CompositionJet 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
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Locations of accelerationLocations 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
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Lessons from B-fieldsInternal to source
• Radio Jet collimation and acceleration is magnetically drivenRadio Knot magnetic fields usually ~ 10 nT ~ 100 μG
• Strong radio polarization indicates B-field compression acceleration
• More complex B-field distributionlower polndepoln in radio
• Use poln to 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
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
B-field configurations
Helical fields generally produce brightness and polarization
distributions in sources which haveasymmetric 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
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
Using polarization to understand jets
Linearly polarized radiation anisotropic B-fields,
Use this + special relativity to find jet geometries + velocities
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
B-field perpendicular @ edges of source Deceleration: Slower at edges than on-axis Boundary-layer entrainment
acceleration deceleration
Cotton et al. ; RL et al.36
Hep 2013 Dr. Nectaria A. B. Gizani HOU
External to source
• Fields around jets: random foreground (rotating plasma in front of emitting material)
Inclination of source matters
M87, Chandra
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Hep 2013 Dr. Nectaria A. B. Gizani HOU
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 momentumTransport
• Fields are not very dynamically important but are significant for thermal conduction
• No evidence for toroidal field confining jets on large scales 38
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