Transcript Talk Outline • Acceleration of particles in AGN  Jets (and containing structures, e.g.

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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 Terminology
Chandra X-ray
cavity
Mathews & Guo
HOST
Lies in intracluster medium (ICM)
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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/e4
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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
Combi & Romero (1997)
UHECR: > 1018 eV
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Radio : synchrotron radn X-rays
from jet and sheath: also
synchrotron (Croston et al.)
X-ray map with radio overlaid
Well-defined NE jet in radio + Xray
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)
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100 GeV γ-rays from
centre and lobes
(Fermi).
Aharonian et al. 2010
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
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Obvious radio jet/X-ray
gas relationship
M 87 (3C 274)
X-rays: Non-thermal
contains strong jet
component
Internal relativistic
motions
Polarization/intensity
correlations → sheared
flow
Radio and X-ray structure:
convective plumes
Chandra X-ray + radio P-b overlaid, ~4”
lifting core material
Residual read-out streak.
→slow entrainment
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M87
Brightest X-ray peaks:
Steep power-law spectra
→synchrotron
VLA
Log-scale
Break frequencies drop
with distance from core
VLA+HST
Knots γmax ≥ 107
Chandra
Linear-scale
HST-1: High variability, like
whole jet, over-pressured
relative to adjacent X-ray
medium, even at
minimum energy
Chandra
+
HST
Marshall et al. (2002)
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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
80 pc from core, optically thin,
brightest region @ 0.6c
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light curve
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Hercules A
MR = -23.75
VLA total intensity distribution
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cm, 1.4 arcsec
optical
z = 0.154
Helical features
Gizani
Ltot ~ 3.81037 W,
HST/WFPC2,
Least,jet~ 1.6×1037 W
Baum et al.Baum
1996 et al.
P178 MHz = 2.3  1027 WHz–1sr–1
Hillas criterion Emax  Ljet1/2
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Collimation of
jets
Gizani & Leahy
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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
Snna , a<0
Gizani & Leahy
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-2 sr-1
0.5 - X-ray,
2 keV, 32´´,
1st cont 2.94
´ 10-10 W
Chandra,
Nulsen
etmal
Lx  ×107 W
Lx point  2×1036 W
b-Fit :
b@ 0.74,
rc @ 121 kpc,
no  104 m-3
dense environment
0.5 < kT (keV) < 1,
NH  6.2×1020 cm-2
Rosat PSPC + HRI , radio overlaid,
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0.3 − 7.5 keV , 2″ resoln
Gizani & Leahy
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Hercules A
VLA B+C+D , 3.6 cm, 0.74 asec, rms ~ 11 mJy,
Gizani & Leahy
~ 6.0 mJy
@ 18 cm: ~41 mJy
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EVN, 18 cm, 0.018 arcsec
35°
1- Gaussian fit
rms 3.6 ×10-4Jy/beam
@ 14.6 mJy
~18.2 × 7 mas
p.a. ~ 139°
Tb @ 2 × 107 K
kpc-jets
New EVN observations scheduled in
June @ 6 + 18 cm
Gizani & Garrett
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3C310
Van Breugel & Fomalont
VLA total intensity distribution
HST/WFPC2 0.05´´
Chiaberge et al.
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
18 with
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radio core
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
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21 cm, 4 arcsec
Global VLBI, 18 cm, phase referencing
4 mas
Natural weighted
10 mas
Gizani & Garrett
20O
~ 130 mJy
Kpc-jets
Gizani
&
Garrett
o
×7. mas
7.3% VLA flux (~10 mJy), pola
Hep~15
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~16.5 mJy
 17× 5 mas
~ 85o
Tb ~ 2.5×107 K
20 -1
Pcore6 cm ~ 7.25 × 1023 WHz
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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.
Owen et al. (1999)
Apparent magnetic field directions.
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Internal B-field
Cont map: I-map, 6 cm, 1.4 arcsec
contours separated by factors 2, 1st at 0.145 mJy/beam
Gizani & Leahy
Projected B-field follows closely edges, jets & ring-like structures in lobes
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Depoln map
DP3.66 , 1.4 ´´; Depoln started in west
DP186 , 1.4´´
Gizani & Leahy
DPl1l2= ml1/mHep
where
l1>lA.2 B., Gizani
m =HOU
p/I, fractional poln
l2 ,2013
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p: polarized intensity, I: total intensity
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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
a1
a2

n(r ) = no ( r ro   ( r ro   , a2 > a1


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
B ( r  = B nm-1
On tangling scales 4  Do (kpc)  35
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2-D
East:-200 RM(rad/m2 )  200
West: RM exceeds ± 500 rad/m2
Bf
i
e
l
d
S
T
R
U
C
T
U
R
E
Gizani
RM = k<f>, f(r = 0.1r0neB×dl Faraday depth, l: line of sight
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Points plotted
if error RM < 5 rad/m
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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
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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
Injected jet may dissipate/heat gas or
support ICM (B-fields) + particles
Central cosmic ray energy
gamma ray production by
πο-decay produced by
protons interacting with ICM
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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 a > 0.5 → diagnostic of acceleration
physics, electron diffusion, and dynamics
• Similar spectra in knots and diffuse emission, but. knot offsets
exist
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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
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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
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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
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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lower polndepoln 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 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
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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
deceleration
acceleration
Cotton et al. ; RL et al.
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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 momentum
Transport
• Fields are not very dynamically important but are significant for
thermal conduction
• No evidence for toroidal
field confining jets on large scales
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