Magnetic fields and jets as particle acceleration sites in active galaxies

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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AGN TerminologyAGN Terminology

HOSTHOST

Lies in intracluster medium (ICM)

Chandra X-rayChandra X-ray

Mathews & Guo

cavity

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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 5


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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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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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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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



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


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.


Co

llim

atio

n o

f C

olli

mat

ion

of

jets

jets


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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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


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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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


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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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


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


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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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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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


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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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


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

Hep 2013 Dr. Nectaria A. B. Gizani HOU 30Hep 2013 Dr. Nectaria A. B. Gizani HOU

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

Hep 2013 Dr. Nectaria A. B. Gizani HOU32

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

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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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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Using polarization to understand jets

Linearly polarized radiation anisotropic B-fields,

Use this + special relativity to find jet geometries + velocities

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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


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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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

Magnetic fields and jets as particle acceleration sites in active galaxies

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