the core of a blazar
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The Core of a Blazar. Alan Marscher Boston University Research Web Page: www.bu.edu/blazars - PowerPoint PPT PresentationTRANSCRIPT
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The Core of a BlazarAlan Marscher
Boston UniversityResearch Web Page: www.bu.edu/blazars
Main collaborators on this effort: S. Jorstad, F. D'Arcangelo, & H. Oh (Boston U.), P. Smith (Steward Obs.), V. Larionov, V. Hagen-
Thorn, & E. Kopatskaya (St. Petersburg State U.), G. Williams (MMO), W. Gear (Cardiff U.), T. Cawthorne (U. Central
Lancashire)
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The Core on VLBI Images
• At one end of jet
• Essentially stationary
• High opacity on upstream side farther downstream at longer (in steps?)
• Low polarization (e.g., 3C 273 on left)
• Some cores: radial polarization matches expected pol. from ambient jet flow with chaotic magnetic field passing through conical shocks (Cawthorne 2006 MNRAS & ...et al., in prep.) (e.g., 1803+784 below)
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Pseudocore & Standing Shocks
"Pseudocore" on VLBI images is either:
1. ~ 1 surface
2. First standing (oblique or conical) shock outside ~ 1 surface
Stationary feature w/ variable pol.
Proposed by Daly & Marscher 1988 ApJ
>1 at ~3 mm
At ~1 cm
>1 at ~4 cm
Pseudocore at ~3 mm
>1 at ~1 cm
Prediction: Moving knots can appear a bit upstream of pseudocore if already loaded with high-E electrons
At ~4 cm
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Quasar 0420-014
7 mm core & optical polarization vector rotated together during 10-day period
turbulent plasma flowing through a standing conical shock produces both 7 mm & optical emission (but some 7 mm also comes from an unpolarized region)
Polarization flipped by 90o during the 10-hr observation
Quasar 0420-014: Optical Emission from Turbulent Core (D'Arcangelo et al. 2007 ApJL)
Scale: 1 mas ~ 8 pc
EV
PA
PO
L %
7mm core (gray)
optical (black)
knot in jet
knot in jet
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Polarization Variations from Turbulence
Apparent rotation of EVPA by >100o occurs ~10% of the time simply from stochastic variations of chaotic field
Signature: EVPA fluctuates about trend, as seen in 0420-014
Other possibilities -- e.g., changing aberration or knot moving down twisting jet - do not agree with behavior of 0420-014
Polarization Variations from Turbulent Plasma Passing through Emission Region
See also T.W. Jones et al.(1985)Simulations with 600 turbulent cells,25 swapped during each time step
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Sketch of Physical Structure of Jet, AGN
Magnetic acceleration zone with toroidal field gives way to turbulence
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Relativistic Gas Dynamical Simulations(2+D)
• Beam of relativistic gas injected from left, flow Lorentz factor =4
• Perturbation initiated in form of momentary increase to =11
• Conical compressions & rarefactions form in wake of disturbance
Click to view movie
Click to view movie
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Pseudocore & "True" Core at mm Wavelengths
"True" core (seen at < ~1 mm): end of flow acceleration zone
Perhaps can probe acc. zone at ~ 1 mm & FIR (see Jorstad et al. 2007, AJ, in press)
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Conclusions
• Polarization variability in 0420-014 conforms with model of turbulent jet plasma flowing through a standing conical shock in the core
→ Such recollimation shocks imply an external confining medium (slower sheath = wind?)
→ Optical & 7 mm emission are partially cospatial
• Long mm-wave observations seem to probe region of jet beyond magnetic acceleration zone
→ Suggestion that 1 mm & FIR emission from this zone
• Standing shocks accelerate electrons that light up moving knots (cf. M87 Cheung et al. 2007)
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Extra Slides
In case the topic comes up during the question period...
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X-Ray Dips in 3C 120
Superluminal ejections follow X-ray dips Very roughly similar to microquasar GRS 1915+105
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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X-Ray Dips/Superluminal Ejections inFR II Radio Galaxy 3C 111
Superluminal ejections follow start of X-ray dips by ~0.3 yr
7 mm core must lie at least 1 pc from black hole to produce the observed X-ray dip/superluminal ejection delay
Complex of new knots following prolonged X-ray/opical low state
FR II Radio Galaxy 3C 111 (z=0.0485) Seems to Do the Same
Scale: 1 mas = 0.92 pc (Ho=70)
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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