3C120

R. Craig WalkerNational Radio Astronomy Observatory

Socorro, NM

Collaborators: J.M. Benson, S.C. Unwin, M.B. Lystrup, T.R.Hunter, G. Pilbratt, P.E. Hardee, D. HarrisVLBA 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, 2002.76Also earlier MarkII observations at 1982.77, 1984.26, and 1989.85

50 pc(80 mas)

• Superluminal and slow moving components• 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 ImageNote 90° rotation

HELICAL INSTABILITIES• Work by Phil Hardee (See poster 17)• The VLBI data constrains:

– Component speeds– Pattern speeds– Brightness distribution

• Model with helical instabilities. Try to determine:– Viewing angle and flow speed– Internal and external sound speeds– Perturbation frequencies

• Goal to learn about jet content and physics.

Psuedo-synchrotron images for low, medium, and high frequency models for hot and warm jets.

Multiple perturbation frequency models from side and from near 14° viewing angle

3C120 VLBA High Resolution• Observations by Gómez, Marscher, Agudo, Alberdi and others• Monthly observations at 22 and 43 GHz with full polarization• 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)

Note Gómez talk this meeting

22 GHz

3C120 from 1" to 30" (VLA 5GHz)

Jet very one-sided

4 knot is subluminal

Note possible helical pattern

25 knot

Core

Dynamic range (peak/rms) ~250,000

Walker Ap. J. 488, 675

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 line-of-sight.

• 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 opposite side (Axon et al., Nature, 341, 631)

-400

400

V

0 20• Hjorth et al see optical jet beyond 4 knot (ApJ 452, L17)

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 northeast

Chandra data is a zero order grating image from Tahir Yaqoob

SUMMARY• 3C120 is a rich source of data

on the jet phenomenon • VLBA monitoring provides

dynamics for comparison with theory– 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