recollimation shock, transverse waves and the whip in bl lacertae
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Recollimation Shock, Transverse Waves and the Whip in BL Lacertae. M.H. Cohen Caltech. M onitoring O f J ets in A ctive Galaxies with V LBA E xperiments. MOJAVE Collaborators. M. Lister (P.I.), J. Richards (Purdue) - PowerPoint PPT PresentationTRANSCRIPT
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Recollimation Shock, Transverse Waves and the Whip in BL Lacertae
M.H. Cohen Caltech
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• M. Lister (P.I.), J. Richards (Purdue)
• T. Arshakian (Univ. of Cologne, Germany)
• M. and H. Aller (Michigan)
• M. Cohen, T. Hovatta, (Caltech)
• D. Homan (Denison)
• M. Kadler, M. Böck (U. Wurzburg, Germany)
• K. Kellermann (NRAO)
• Y. Kovalev (ASC Lebedev, Russia)
• A. Lobanov, T. Savolainen, J. A. Zensus (MPIfR, Germany)
• D. Meier (JPL)
• A. Pushkarev (Crimean Observatory, Ukraine)
• E. Ros (Valencia, Spain)
MOJAVE Collaborators Monitoring
Of
Jets in
Active Galaxies with
VLBA
Experiments
Very Long Baseline Array
The MOJAVE Program is supported NASA Fermi Grant NNX08AV67G
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BL Lac Topics
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• Components, Ridge Line• Recollimation Shock• PA Variations: Wobble• Transverse Waves• Wave Speeds• Relaxation in 2010: Wiggle• Conclusions
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Components
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• Components are a small number of elliptical Gaussians that sum to the image. They usually are circular.• A component is often a bright spot in the image.• Components are tracked in time, if the cadence of observations is fast enough.
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Ridge Line
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• BL Lac is elongated and has a ridge.
• Most components move downstream• along the ridge (±0.1 mas)
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Ridge Line and Components
2006.862005.71
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Several New Components per YearMax Speed 10.6c
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BL Lac Component Tracks
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quasi-stationaryrecollimation shock
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Recollimation Shock
• Component 7 = recollimation shock
• Analogy to M87, 3C120
• Simulation (Lind et al 1999, ...) shows a‘magnetic chamber’ and fast cpts ejected into a ‘nose cone’ (not full 3D RMHD) (Meier p715)
• Need strong toroidal component in the magnetic field
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z vmax dist from core
• 3C 120 0.033 5.3c ~ 5 mas 3.1 * 80 mas ~ 3x107 rg
• M 87 .00436 4.3 ** >= 106 rg • BL Lac .0686 10.6 # ~ 106 rg
* downstream from C1 Agudo et al 2012** downstream from HST1 Cheung et al 2007# downstream from cpt 7 MOJAVE
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Recollimation Shock II
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BL LacPosition Angle vs Epoch
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V ≈ 1.15 mas yr-1
≈ 4.8 c
Transverse Wave 2004 - 2007
A
B
A
B
Shifted Ridge Lines
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Transverse Waves 1999-2000
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V ≈ 0.80 mas yr-1
≈ 3.3 c
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Transverse Wave 2000-2001
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Component 16 Advected with the Transverse Wave
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Several New Components per YearMax Speed 10.6c
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BL Lac Component Tracks
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quasi-stationaryrecollimation shock
CenterlinePA=166o
BL Lac 2010.8-2012.8wiggle
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PA ≈ 171o
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• Strong quasi-stationary component is identified as a recollimation shock.• Distance from core ~ 106 rg
• Superluminal components appear to come from or through the recollimation shock.
BL LacConclusions I
BL LacConclusions II
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• Jet supports transverse waves.• Waves have superluminal speed.• Waves are correlated with swings in the inner PA.• Components are advected with the transverse motion.• Jet acts more like a rope than a water hose.• When wave activity dies down, a stable wiggle appears.
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These observations support a model in which the jet contains a strong toroidal magnetic field. Transverse waves (Alfven?) are excited by PA swings of the nozzle, and propagate superluminally downstream, as large-scale wiggles on the ridge line. The superluminal components (fast MHD waves?) stay on the ridge, and can be advected transversely. In 2009 the waves died down, and a small-scale stationary wiggle appeared on the jet.
Conclusions III