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