Kinematics of AGN Jets

1
Kinematics of AGN Jets

• Ken Kellermann, NRAO
• with
• Matt Lister, Dan Homan, Yuri Kovalev, Marshall
  Cohen, Matthias Kadler
• and the
• MOJAVE team
• Approaching Micro-Arcsecond Resolutionwith
  VSOP-2 Astrophysics and Technology

2
Outline of talk

• Multi-epoch programs
• 2.3, 5, 8, 15, 43 GHz
• Comparison with relativistic beaming models
• Intrinsic parameters (luminosity, Lorentz
  factors, Doppler factors)
• Specific selected sources
• AGN kinematics
• New opportunities
• VLBA/EVN
• GLAST
• VSOP-2
• RadioAstron

3
Multi-epoch VLBA Programs

• 5 GHz (Britzen et al., submitted to AA)
• Velocities for 237 CJF sources from 3 to 5
  epochs from 1990-2000
• (2.3) 8 GHz RRFID (Piner et al. 2007, AJ, 133,
  2357)
• VLBA up to 7 other antennas
• 500 sources including 2.3 GHz
• 87 sources at 8 GHz 1994 1998 analyzed
• 15 GHz
• VLBA 2cm Survey (Cohen et al. 2007 ApJ 658, 232
  Kellermann et al. 2004, ApJ 609, 539)
• 110 AGN - 1994-2001
• MOJAVE (Lister Homan, 2005, AJ 130, 1389)
• 192 sources including polarization
• 133 complete sample
• 59 other special sources (? ray, interesting
  kinematics)
• Up to 12 years and up to 30 (54) epochs bends
  and accelerations
• 22 43 GHz (Jorstad et al. 2001, ApJS 134, 181
  AJ 130, 1418 2005, 130, 1418)
• Monthly and bi-monthly images but smaller samples
• Gamma-Ray blazars
• Some recent selected single source detailed
  studies
• 3C 120 (Walker et al, 2001, ApJ 556, 772)

4
Questions

• How and where does the relativistic flow form and
  get collimated and accelerated to vc?
• Are there accelerations or decelerations?
• How does the flow vary across the jet?
• Is there evidence for a two layer flow?
• What is the confinement mechanism?
• How do relativistic jets interact with their
  environment?
• What is the source of gamma-ray emission?
• Why are only some blazars gamma-ray sources
• What is the mechanism for gamma-ray production
• What is the relation, if any between the
  gamma-ray and radio emission
• Where does the gamma-ray and X-ray emission
  originate?
• What are intrinsic Lorentz factors, luminosity,
  Tb of the relativistic jets?
• What determines these values?
• Is the velocity related other observables? e.g.,
  radio, optical, ?-ray luminosity or variability?
• Does the apparent pattern velocity reflect the
  true bulk velocity of the relativistic flow?
• Many jets are curved.
• Do different jet features follow the same
  trajectory?
• Is the motion ballistic (rotating nozzle)?

5
But .

• Early VLBI measurements determined a single
  velocity
• Different beams not the same at all epochs
• VLBA highly repeatable results
• 5 to 10 years of data
• 5 to 10 epochs
• We do not obtain simple snapshots of the jets
• We observe different parts of the source at
  different time
• Superluminal motion
• Distortion of angles
• We do not observe relativistic flow directly
• Instead we observe component motions in
  multi-epoch observations
• model fitting in u,v plane
• component location in image plane
• Components may reflect propagation of shocks not
  the underlying bulk relativistic flow
• Components may not remain stable, but may break
  up into sub-components
• Or separate components merge
• Not all parts of the jet move with the same speed

6
Determination of Intrinsic Parameters

• We observe Tapp, ßapp vapp/c, and Lapp
• We want to determine Tint, ?, Lo, ?, and d

Lapp/Lo d2 d ?-1(1-ßcos ?)-1 ?(1-
ß2)-1/2 ßobs ßsin?/(1-ßcos ?) Tobs d x Tint
Inverse Compton Limit Tint 1011.5 K
Ee gtgt Em (Kellermann and Pauliny-Toth, 1969, ApJ,
155, L71) Equipartition Temperature Tint
1010.5 K Ee Em (Readhead, 1994, ApJ, 426,
51)
7
Tobs d x Tint

• Tobs depends only on baseline length and
  accuracy, independent of wavelength
• Tmax (1 Jy) for terrestrial baselines 1012-13 K
• VLBA
• Tmax up to 5 x 1013 K
• Kovalev et al. 2005, AJ, 130, 247
• Best way to detect relativistic beaming
• is to go to space
• HALCA
• Tmax up to 1014 K
• Horiuchi et al. ApJ. 616 (2004) 110-122
• d 100 to 1000 (if Tint 1011-12)
• Implies d ? 50 to 500?
• Maybe?
• More likely transient value
• Other

8
Compare ß and Tobs

• Highest velocities are observed in sources with
  high brightness temperature.
• There are no fast sources with low brightness
  temperature.
• Along ? ?crit 1/ ? d ß Tobs ßTint
• Simulation N(?) a ?-1.5
• With Tint allowed to vary
• High state
• Tint 2 x 1011K Ep/Em 105
• Normal state
• Tint 3 x 1010 K Ep/Em 1

high
?30
normal
?30
Homan et al., 2006, ApJ 642, L115
9
Variability brightness temperature
UMRAO

• diameter lt c t
• ? lt diameter/Distance
• Tvar gt S?2/2k ?2
• Tvar d3Tint
• dvar (Tvar/Tint)1/3

10
Apparent speed vs. variability Doppler factor
Dvar based on 8 mm Metsahovi observations
adapted from Kellermann, et al. 2004, ApJ 600,
539
Dvar (Tvar/ Tint)1/3
?32
?max 32
Tint 2 x1010 K close to value from direct
observation of T
11
Cohen et al. 2007, ApJ 658, 232
?c1/ ?
Low luminosity, low speed sources are not blazers
beamed in the plane of the sky, but are
intrinsically slow and intrinsically less luminous
?
Lint1025 ?32
Cohen et al. ApJ, in press (astro-ph 0611642)
12

• M87 is one of the closest relativistic jets
• 1 mas ? 0.08 pc 1 mas/yr ? 0.25c
• Shklovsky (1964) suggested differential Doppler
  beaming to explain observed asymmetry of the
  optical jet
• But at 2 cm Kovalev et al., 2007, (ApJ, 668, 27)
  found ß lt 0.05c within 20 mas (1.6 pc) of jet
  base
• Jet is intrinsically asymmetric, or
• The observed slow component motion does not
  reflect the bulk flow
• Cheung et al. (2007, ApJL 663, L65) observe ß
  4.5 near HST-1 (60 pc downstream)
• Is HST-1 the source of TeV emission?
• Kovalev et al do not see any evidence of HST-1
  with mas resolution in 2000
• Evidence for two layer (spine-sheath) flow

13
3C 279
3C 279

• µ Changed from 0.25 to 0.40 mas/yr
• v Changed from 8c to 13c and ??app 260
• corresponds to increase in ? 1deg
• Change occurs 30 pc down the jet
• Deprojected bend 1 kpc downstream
• Doppler Factor 30
• Homan et al. 2003, ApJL 589, L9

14

• 0738313
• Motion along a constant
• curved trajectory

1308326 Jet ejection from an apparent
precessing nozzle ß22
ß lt 8
Lister, 2007, 209th AAS, Seattle, WA
15
3C 111

• Outburst breaks up into multiple trailing
  components probably reflecting advancing and
  trailing shocks
• Kadler et al. ApJ submitted

1990
2000
16
AGN Kinematics

• Blazar jets are highly relativistic and pointed
  nearly toward observer
• Apparent motion may depend critically on viewing
  angle
• Each jet has a characteristic velocity which may
  reflect the bulk flow
• Low luminosity AGN are slow (v/c)app 1
  (70c)
• Quasars are fast v/c 8 (99c)
• Apparent velocities (?) up to about 35c (99.9c)
  are observed
• Only the most luminous sources have large Lorentz
  factors
• But, subluminal and stationary components are
  also observed
• Gamma-ray sources (EGRET) tend to have a somewhat
  higher ß
• The relativistic flow is complex and no simple
  picture covers all sources
• Initial collimation and acceleration takes place
  close to the central engine but collimation
  events occur 1 kpc away possibly due to
  interaction with ISM.
• Both accelerations and decelerations are observed
  along the jet
• Changes in speed (increase) and direction if
  individual components
• But, systematic decrease in velocity with
  distance (wavelength 0.7, 2, 6 cm)
• In situ acceleration may be important along the
  jet (M87)

17
AGN Kinematics-cont

• Tobs up to 1014 K
• Initially Ee gtgt Em
• Quickly Tobs approaches equilibrium (Tb lt IC
  limit)
• Simple ballistic models do not work
• Non-radial motions are not uncommon
• Motions sometimes (not always) follows
  pre-existing channels (Lister, 2001, ApJ 562,
  208)
• Evidence for a rotating nozzle or helical motions
  (1308326, 3C 120)
• There is some evidence that the ejection of new
  components is associated with a radio (Savolainen
  et al. 2002, AA 394, 851) or ?-ray event
  (Jorstad et al. 2001, ApJS 134, 181)
• There is a broad distribution of Lorentz factors
  among sources
• Parent population of jets mostly mildly
  relativistic P(?) a ?-1.5
• Due to Doppler bias we see mostly
  ultra-relativistic jets, but slower jets are also
  directly observed.
• Analysis is complicated by
• Components splitting and merging
• possible different pattern and bulk velocities
• finite opening angle (Gopal-Krishna et al, 2006,
  MNRAS 369, 1287)
• velocity gradients across the jets

18
New opportunities

• Perhaps a factor of 5 improve in VLBA sensitivity
• e-MERLIN working with EVN to give excellent
  surface brightness sensitivity
• GLAST ? ray connection
• How do the motions relate to ?-ray events?
• Is there a change in ?-ray luminosity associated
  with radio ejection
• Where does the ?-ray emission occur?
• MOJAVE includes- EGRET and up to 100 new GLAST
  ?-ray sources
• VSOP-2
• 3 to 4 times improvement in resolution
• Will observe even closer to central engine
• for nearby sources such as M87 close to accretion
  disk
• Excellent time sampling will be necessary
• AGN jets are mostly smooth
• Good u,v coverage and good sensitivity necessary
• RadioAstron 2009 launch?
• Even better resolution 10x VSOP-2
• Poor imaging capability
• Will measure Tb up to 1016 K
• If they exist?