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                         R. Craig Walker
           National Radio Astronomy Observatory
                       Socorro, NM
Collaborators: J.M. Benson, S.C. Unwin, M.B. Lystrup,
  T.R.Hunter, G. Pilbratt, P.E. Hardee, D. Harris
 VLBA 10th Anniversary                     June 9, 2003
          Why 3C120?
• Quasar-like properties but “nearby”
  – z=0.033 D~125 Mpc Scale: 0.6 pc/mas
  – One of closest superluminals
     • High angular rates (2.5 mas/yr)
     • Prime monitoring candidate
  – Large (~1') optical galaxy with emission lines
     • Underlying structure unclear – “train wreck”
• Jet detected in optical and x-ray
• Long history of observations

                    HST images obtained from archive by D. Harris and T. Cheung
                3C120 VLBA 1.7 GHz
                 Monitoring Project
        Observations so far: 1994.44, 1997.70, 2000.68, 2002.76
           Also earlier MarkII observations at 1982.77, 1984.26, and 1989.85
50 pc              • Superluminal and slow moving components
(80 mas)
                   • Possible helical pattern at 50 pc (80 mas)
      Helical Pattern
• Pattern near 50 pc (80 mas) looks like helix in
  projection and is moving slowly
    – Superluminal features move through it
• Simple “beads on a string” model requires
  extremely small angle to line-of-sight
• Reasonable geometry if high pressure (high
  brightness) region is toward outside of jet
    – Pattern follows wider opening angle helix than
      individual particles
    – Expected from instability theory
Preliminary Polarization Image
                  Note 90° rotation
• Work by Phil Hardee (See poster 17)
• The VLBI data constrains:
    – Component speeds
    – Pattern speeds
    – Brightness distribution
• Model with helical instabilities. Try to
    – Viewing angle and flow speed
    – Internal and external sound speeds         Psuedo-synchrotron images for low,
    – Perturbation frequencies                   medium, and high frequency models for
• Goal to learn about jet content and physics.   hot and warm jets.

models from
side and from
near 14°
viewing angle
 3C120 VLBA High Resolution                                                                  Note
                                                                                           Gómez talk
• Observations by Gómez, Marscher, Agudo, Alberdi and others                               this
• Monthly observations at 22 and 43 GHz with full polarization                             meeting
• Have shown evidence for:
    – Flashing components: External interactions (Gómez et al., Science 289, 2317)
    – Trailing components: Shock physics (Gómez et al., Ap. J. 561, L161, Agudo et al., Ap. J. 549, L183
    – Xray correlation: X-ray dip at component ejection (Marscher et al Nature 417, 625)
• Also monitored at 15 GHz by Homan, et al.               (Ap. J. 549, 840)

                                                                                           22 GHz
   3C120 from 1" to 30" (VLA 5GHz)
                                Walker Ap. J. 488, 675

                     25 knot

Jet very one-sided

    4 knot is
Core                   Note possible helical pattern

                     Dynamic range (peak/rms) ~250,000
     HST –VLBI/MERLIN – VLA Overlay
• Radio knot at 4 has
  optical (and x-ray)
  counterparts on what
  looks like a spiral arm.
• Superluminal motion in
  inner radio jet implies
  that the jet is close to the
• Is the “spiral arm” along
  the line-of-sight? The
  rest of the galaxy looks
  face on. Is it a tidal tail?
• Low spatial resolution
  optical spectra are
  double peaked near the
  knot – and on the                                            400
  opposite side (Axon et al.,
 Nature, 341, 631)                                             V

• Hjorth et al see optical jet beyond 4 knot (ApJ 452, L17)   -400   0   20
Chandra X-ray Detections
• X-rays seen at core, 4 and 25 knots, jet near 8
• Diffuse x-rays and weak radio near 25 knot (right)

                                                                      • Probably synchrotron
                                                                        emission at 4 knot
                                                                      • Emission mechanism
                                                                        at 25 knot is a
                                                                        puzzle, especially in
                                                                        the diffuse region to
       Chandra data is a zero order grating image from Tahir Yaqoob
• 3C120 is a rich source of data
  on the jet phenomenon
• VLBA monitoring provides
  dynamics for comparison with
   – High frequency observations of
     inner few pc
   – 1.7 GHz observations of helical
     pattern at 50 pc
• Optical: possible interaction
  with spiral arm or tidal tail at
  4" knot
• X-ray: emission mechanism
  puzzle at 25" knot

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