AGN Jets: A Review for Comparison with Microquasars

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AGN Jets A Review for Comparison with
Microquasars GRBs

• Alan Marscher
• Boston University
• Research Web Page www.bu.edu/blazars

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Emission Regions in a Radio-Loud AGN
Differences with BH X-ray binaries Inner
accretion disk not hot enough to emit X-rays (but
can have X-ray emitting ADAF if accretion rate is
low) ? harder X-ray spectrum Core is always
present in nearly all radio-loud AGN jets
Unbeamed
Beamed
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Jets of Low-Luminosity AGNs
Seyfert
Liners
Jets often seem to be interacting with
clouds Apparent motion usually lt c
III Zw 2 (Brunthaler et al. 2005, AA, 435, 497)
0.6c at 15 GHz, 1.2c at 43 GHz
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Blazar Jets 3C 279
Superluminal motion between 5c 20c, bulk
Lorentz factor up to 25, Doppler factor up to
50 Changes in apparent speed may be due solely
to change in direction of jet by about 2o
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Blazar Jets PKS 1510-089
Apparent speeds up to 45c (fastest known blazar
containing well-defined superluminal knots) ?
bulk Lorentz factor of at least 45 in jet
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Radio-Loud AGN The General Population

• Relativistic beaming causes strong selection
  effect in flux-limited radio surveys ? Bias
  toward high-? jets pointing almost directly along
  line-of-sight
• Population simulation (Lister Marscher 1997)
  observed apparent-motion redshift distribution
  reproduced if
• Radio-galaxy luminosity function measured at low
  z is valid at higher z
• 2. Lorentz factor distribution is a power law,
  N(?) ? ?-a, a 1.5-1.75, with a high- ? cutoff
  of 45 (highest observed ?app)
• ? 12-17 of jets in population have ? 10-45
• 5-7 have ? 20-45, 2-3 have ? 30-45,
  0.5-0.9 have ? 40-45
• Spine-sheath models for compact AGN jets
  requiring a very high-? spine in a typical jet
  are untenable unless radiation from the spine is
  suppressed
• - But such ultra-fast spines should be
  prodigious emitters of inverse Compton X-rays off
  ambient photon field (e.g., CMB)

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Intrinsic Half Opening Angles of Jets (Jorstad
et al. 2005, AJ, 130, 1418)
Side-on radio galaxies Opening angles typically
1-4o

• Blazars
• ? 1/?
• Agrees with models in which jet is focused as it
  is accelerated over an extended region.(HD
  Marscher 1980 MHD Vlahakis Königl 2004)
• Explains why apparent opening angle is
  uncorrelated with apparent speed

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Knots in Jets
Polarization BL Lac objects usually have B
transverse to local jet axis well downstream of
core
stationary
8c
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Knots in Jets
Polarization Quasars generally have oblique
direction of B after aberration taken into account
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Shock Model for Knots in Jets
Best-liked model Shocks propagating down
turbulent jet Magnetic field compressed at shock
front Electrons accelerated at shock
front Polarization indicates that in general
such shocks must be oblique, especially after
correcting for aberration Need supersonic
relative motion to get shock waves ? strong
shocks are difficult for high-? flows with
relativistic equation of state (but dont need
very strong shocks for substantial enhancement of
radiation)
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Bends in Jets
Bending Apparent bends amplified greatly by
projection effects Intrinsic bends by only a few
degrees
3C 446
0528134
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Changes in Direction
Change in apparent speed can be due solely to
change in direction Nonthermal luminosity seems
to be related to direction of jet Changes
amplified greatly by projection effects Velocity
seems ballistic in some jets but seems to follow
twisting jet in many others
Changes in direction appear to be abrupt, unlike
precession (more like an unstable firehose)
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The Core of Blazar Jets

• Frequencies below 40 GHz ? 1 surface
• At higher frequencies
• a. Conical standing shock? (Daly Marscher 1988)
• - See poster by Cawthorne et al. (e.g., 1803784
  shown below)
• In favor reproduces polarization pattern if
  randomly oriented B field is compressed by
  conical shock
• b. End of zone of accelerating flow
• - Where Doppler factor reaches asymptotic value

1803784
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Jet Acceleration over Extended Region
Theory A jet with ? gt 10 cannot propagate out
of nuclear region (Phinney 1987)
HD Pressure gradient p ? r-a Lorentz factor
increases with cross-sectional radius R G? R ?
p-1/4 ? ra/4 If a lt 4/(3?1) and viewing angle is
small, brightest emission is where G reaches its
asymptotic value If viewing angle is large,
brightest emission is at lowest r where high-E
electrons are accelerated (Marscher 1980 ApJ)
MHD Models still being developed Vlahakis
Königl (2004, ApJ) solution appears similar to HD
solution, except that G decreases away from jet
axis there is no distinct boundary
Predicts toroidal field, but perhaps only close
to central engine, where opacity is too high to
image
In either case, energy density at base of jet
must exceed 2G?c2 Might require a magnetosphere
(pulsar or ergosphere of spinning BH)
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Cygnus A (Bach et al. 2004, 2005)FR II radio
galaxy, jet at large angle to l.o.s.
Counter-core
Core
Gap between core counterjet lt 0.7 mas Apparent
speed increases with distance from core
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Evidence for Collimation of Jets Well Outside
Central Engine

• VLBA observations of M87 jet appears broad near
  core
• ? Flow appears to be collimated on scales 1000
  Rs

Junor et al. 2000 Nature
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The FR I Radio Galaxy 3C 120 (z0.033)
Sequence of VLBA images (Marscher et al. 2002)
Scale 1 mas 0.64 pc 2.1 lt-yr (Ho70)
HST image (Harris Cheung)

• Superluminal apparent motion, 5c (1.8-2.8
  milliarcsec/yr)
• X-ray spectrum similar to Seyferts
• Mass of central black hole 3x107 solar masses
  (Marshall, Miller, Marscher 2004 Wandel et al.
  1999)

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X-Ray Dips in 3C 120
Superluminal ejections follow X-ray dips ?
Similar to microquasar GRS 1915105
Radio core must lie at least 0.4 pc from black
hole to produce the observed X-ray
dip/superluminal ejection delay of 60 days
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Comparison of GRS1915105 with 3C 120 Light Curves
? BH mass of 3C 120 2x106 times that of GRS
1915105, so timescales of hours to months in the
former are similar to the scaled-up quasi-periods
(0.15 to 10 s) duration of X-ray dips in the
latter. ?Typical fractional amplitude of dips is
also similar ? Long, deep dips not yet seen in 3C
120
150 s of blow-up should scale up to 10 yr in 3C
120 if timescales ? Mbh Below X-ray light curve
of 3C 120 over 2.2 yr
blow-up
? GRS 1915105 over 3000 s on 9/9/97 Light curve
(top) PSD (bottom) (Taken from Markwardt et al.
1999 ApJL) Perhaps low-hard X-ray state
corresponds to 3C 120
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FR II Radio Galaxy 3C 111 (z0.0485) Seems to Do
the Same
1 mm flare
May 2004
1 milliarcsec
August2004
New knot
Superluminal ejection follows minimum of deep
X-ray by 0.3 yr
Radio core must lie at least 0.4 pc from black
hole to produce the observed X-ray
dip/superluminal ejection delay
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Accretion States of AGNs

• Power spectral density of Seyferts similar to
  high-soft state of Cygnus X-1 (McHardy et al.
  2004)
• Weak jets of Seyferts consistent with weak/no jet
  in high-soft state of GRS1915105 (Fender
  Belloni 2004)
• Inner accretion disk not hot enough to emit
  X-rays ? spectrum not so soft (mean spectral
  index of 0.9)
• X-ray spectra of radio galaxies 3C 120 (FR 1)
  3C 111 (FR 2) flatter than this
• - Suggestive of low-hard state with steady,
  optically thick jet seen in GRS1915105
• Liners and low-luminosity Seyferts may have ADAFs
  near black hole

Seyfert PSDs from McHardy et al. (2004)
High break timescale scales approximately
linearly with mass
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Sketch of Physical Structure of Jet, AGN

CORE
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Relation of AGN jets to XRBs GRBs

• Bulk Lorentz factors of jet flows can exceed 40c
  - not too dissimilar to GRBs - but only rarely
• ? Ultra-fast (? gt 10) spines cannot be general
  feature in AGN ? Blandford-Payne type jet
  launching might be sufficient in high fraction of
  AGN
• X-ray variability of high-luminosity Seyferts has
  similar PSD to XRBs in high-soft state, with weak
  jets
• X-ray spectrum of radio galaxies with strong jets
  flatter than in Seyferts, similar to low-hard
  state
• Evidence for acceleration focusing of jet over
  an extended region is mounting
• ? Conforms with HD some MHD models for jet
  launching