The Core of a Blazar
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Transcript of The Core of a Blazar
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)
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)
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
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
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
Sketch of Physical Structure of Jet, AGN
Magnetic acceleration zone with toroidal field gives way to turbulence
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
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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)
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)
Extra Slides
In case the topic comes up during the question period...
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
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)
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