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

Physical Properties of 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 β app ~ 10 or larger -> Γ > 10 are common • But an even larger population with smaller Lorentz factors. • Decline in histogram above β app ~ 10 implies a power-law Lorentz factor distribution (Lister et al. 2009) • Max observed Speed ~ Maximum Γ (e.g. Lister & Marscher 1997) � Γ max ~ 50 for Blazar Jet Population

Lessons from Speed Distributions? • Many jets have β app ~ 10 or larger -> Γ > 10 are common • But an even larger population with smaller Lorentz factors. • Decline in histogram above β app ~ 10 implies a power-law Lorentz factor distribution (Lister et al. 2009) • Max observed Speed ~ Maximum Γ (e.g. Lister & Marscher 1997) � Γ max ~ 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 β app -> 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 3C 273 Asada et al. 2002 Multiple Scales and Epochs: Zavala & Taylor 2005; Attridge et al. 2005 with mm VLBI; Asada et al. 2008

MOJAVE Multi-band observations: 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 10 18 A in 3C303 by Kronberg et al. 2011 (astro-ph 1106.1397)

MOJAVE: Quasar 0333+321 (NRAO 140) z = 1.26 Circular Polarization 2005-09-23 20 pc

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 of 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 ≤ γ l ≤ 35 • Strong poloidal magnetic field in core of jet: Estimated flux: 2 x 10 34 - 1 x 10 35 G cm 2 • 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, Γ max ~ 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.) • Tigran Arshakian (MPIfR) • Talvikki Hovatta (Caltech), • Andrew Lobanov (MPIfR) • Preeti Kharb (R.I.T.), • Alexander Pushkarev (Pulkovo/CrAO) • Yuri Kovalev • Tuomas Savolainen (MPIfR) • Tony Zensus (MPIfR) (Lebedev Physical Inst) • Dan Homan (Denison Univ.) • Eduardo Ros (Univ. of Valencia) • Ken Kellermann (NRAO) • Matthias Kadler • Hugh Aller (Univ. of Michigan) • (Univ. Erlangen-Nuremberg) • Margo Aller (Univ. of Michigan) • Neil Gehrels (Goddard) • Marshall Cohen (Caltech) • Julie McEnery (Goddard)