Physical Properties of Jets in AGN Dan Homan Denison University - - PowerPoint PPT Presentation

Physical Properties

• f Jets in AGN

Dan Homan Denison University

Probes of Physical Properties

• (Part 1) Long Time Baseline Kinematics
• Distribution of Apparent Speeds in Blazar Population
• Lorentz Factor/Viewing Angle
• Proxy for Doppler factor?
• Changes in Speed and/or Direction
• Jet Acceleration, Bending, Collimation
• Tracing Out Broader Jet Structure
• Variation in Jet Ejection Angles
• Apparent Opening Angle
• - Sensitive to Viewing Angle + Intrinsic Opening Angle

Lessons from Speed Distributions?

• Many jets have βapp ~ 10 or larger -> Γ > 10 are common
• But an even larger population with smaller Lorentz factors.
• Decline in histogram above βapp ~ 10 implies a power-law Lorentz

factor distribution (Lister et al. 2009)

• Max observed Speed ~ Maximum Γ

(e.g. Lister & Marscher 1997)

Γmax ~ 50 for Blazar Jet Population

Lessons from Speed Distributions?

• Many jets have βapp ~ 10 or larger -> Γ > 10 are common
• But an even larger population with smaller Lorentz factors.
• Decline in histogram above βapp ~ 10 implies a power-law Lorentz

factor distribution (Lister et al. 2009)

• Max observed Speed ~ Maximum Γ

(e.g. Lister & Marscher 1997)

Γmax ~ 50 for Blazar Jet Population

• Study of individual components by Jorstad et al. (2005)

estimated δ from fading times of components in 15 jets: δ and βapp -> Γ

• Found Γ ranged from 5 to 40
• for most quasar components Γ ~ 16 -18 (Gamma-ray Blazars)
• Hovatta et al. (2009) found δ from variability brightness

temperatures

• Median Γ = 14 and θ = 4 degrees

Changes in Apparent Motion

• Acceleration
• Collimation/Bending
• Variation in Jet Ejection Angle
• Show Movies: 1222+216, 3C279, 1308+326

Acceleration

Parallel Acceleration Perpendicular Acceleration

If Only Speed Changes….

Can we constrain from VLBI observations?

Examples

Acceleration Results

• Analysis of 203 jet components from

MOJAVE sample (Homan et al. 2009)

• Parallel Accel > Perp. Accel on average
• Real changes in speed of jet components, not just

changes in direction

• ~ 25% of components have
• Accelerating components tend to be at shorter

projected distances than Decelerating components

• Jorstad et al. (2005) see accelerations in jet components

close to base of their jets

• 50% of components show non-radial motion,

usually in the direction of downstream emission

Many Components in Some Jets

Lister et al. 2009

Multi-Epoch Stacked Images: 3C273

Multi-Epoch Stacked Images: 1308+326

Distribution of Jet Opening Angles

• Pushkarev et al. 2009
• FERMI LAT detected jets

have somewhat larger apparent opening angles

• Intrinsic Opening angles
• Quasar mean: 1.2 ± 0.1 deg.
• BLLac mean: 2.4 ± 0.6 deg.

Probes of Physical Properties

• Polarization and Spectral Studies of Parsec-Scale Jets
• 3-D magnetic field structure of jets?
• Role in collimation & acceleration of jets
• Connection with SMBH/Accretion Disk?
• Low energy particle population
• Particle acceleration mechanisms
• Particle content & kinetic luminosity of jets
• Tracer of jet flow and hydrodynamics
• Shocks -- sites of active conversion of bulk kinetic energy
• Shear, Aberration, etc…
• Probe of material + fields external to jets
• Sheath or boundary layers
• Narrow line region

MOJAVE: Quasar 0333+321 (NRAO 140) z = 1.26

2005-09-23

20 pc Apparent Speed = 12.8c (Lister et al. 2009)

Polarization as a Probe of Jet B-fields

• Fractional Linear Polarization
• Jet Cores ~ few percent up to 10%
• Jet Features ~ 5-10% up to few tens of percent
• Magnetic Field Order on Parsec Scales?
• Likely dominated by tangled magnetic fields
• Oblique shocks may play important role (e.g.

Marscher et al. 2002, Hughes et al. 2011)

• Are there larger scale, ordered components to the

jet field: Toriodal, Poloidal, Helical?

Faraday Rotation

Zavala & Taylor 2001

Rotation Measure Gradients

Asada et al. 2002 3C 273 Multiple Scales and Epochs:

Zavala & Taylor 2005; Attridge et al. 2005 with mm VLBI; Asada et al. 2008

MOJAVE Multi-band

• bservations:

8.1, 8.4, 12.1, 15.3 GHz Hovatta et al., in prep.

TeV Blazar: Markarian 501

(Croke et al. 2010)

Other Jets:

Gabuzda et al. 2004; Asada et al. 2008; Gomez et al. 2008; O’Sullivan & Gabuzda 2009; Mahmud et al. 2009; Asada et al. 2010

Evidence for Helical/Toriodal Fields?

• Gradients in Faraday Rotation Across Jets…
• Due to Toroidal field structures within jets or in a

boundary layer surrounding them?

• Could they be due to external pressure gradients?
• If Toroidal Fields…
• Role in Collimation & Acceleration
• Jets carry a current (where is it… how does it flow?)
• Estimate of 1018 A in 3C303 by Kronberg et al. 2011

(astro-ph 1106.1397)

2005-09-23

20 pc

MOJAVE: Quasar 0333+321 (NRAO 140) z = 1.26

Circular Polarization

MOJAVE-I CP Results

• Circular Polarization detected (≥ 3 σ) in at

least one epoch in 54 of 133 jets

• Wide variety of variability behavior
• No clear correlation between linear and circular

polarization

• Sign Preference?
• 20 jets have multiple epoch ≥ 3 σ detections

Only 1/20 changes sign

• 49 jets have multiple epoch ≥ 2 σ measurements

Only 2/49 change sign

Core Region of 3C279

Polarization Model

• f Components 5

and 4

Multi-band Radiative Transfer

• For Jet components and Jet core in 3C279

(Homan et al. 2009)

• Relativistic low energy cutoff: 5 ≤ γl ≤ 35
• Strong poloidal magnetic field in core of jet:

Estimated flux: 2 x 1034 - 1 x 1035 G cm2

• Jet is dynamically dominated by protons.

Summary (part 1)

• Long Time Baseline Proper Motion Studies
• Distribution peaks near 10c, extends up to 50c

➡ Γ > 10 are common, Γmax ~ 50

• Likely a power-law distribution of Γ in parent pop.
• Wide Apparent Opening Angles
• Intrinsic opening angles ~ 1-2 degrees on average
• Changes in Speed/Direction of Jet motion common
• Flow is often non-ballistic - follow pre-existing channels
• Genuine speed changes in addition to changes in direction
• Deceleration more common further from the jet base

Summary (part 2)

• Polarization Studies of Parsec-Scale Jets
• B-fields likely dominated by tangled magnetic

fields which are shocked/sheared hydro- dynamically

• FR reveals fields/particles close to/within the jet
• Apparent gradients might be evidence for toroidal

field components

• Circular Pol. Probes fields/particles within jet
• Full Stokes Radiative transfer needed over several

frequencies

MOJAVE Team

• Matt Lister -- P.I. (Purdue Univ.)
• Talvikki Hovatta (Caltech),
• Preeti Kharb (R.I.T.),
• Yuri Kovalev

(Lebedev Physical Inst)

• Dan Homan (Denison Univ.)
• Ken Kellermann (NRAO)
• Hugh Aller (Univ. of Michigan)
• Margo Aller (Univ. of Michigan)
• Marshall Cohen (Caltech)
• Tigran Arshakian (MPIfR)
• Andrew Lobanov (MPIfR)
• Alexander Pushkarev (Pulkovo/CrAO)
• Tuomas Savolainen (MPIfR)
• Tony Zensus (MPIfR)
• Eduardo Ros (Univ. of Valencia)
• Matthias Kadler
• (Univ. Erlangen-Nuremberg)
• Neil Gehrels (Goddard)
• Julie McEnery (Goddard)