Physical Properties of Jets in AGN. Dan Homan Denison University

Transcription

1 Physical Properties of Jets in AGN Dan Homan Denison University

2 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

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5 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

6 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 ~ (Gamma-ray Blazars) Hovatta et al. (2009) found δ from variability brightness temperatures Median Γ = 14 and θ = 4 degrees

7 Changes in Apparent Motion Acceleration Collimation/Bending Variation in Jet Ejection Angle Show Movies: , 3C279,

8 Acceleration Parallel Acceleration Perpendicular Acceleration

9 If Only Speed Changes. Can we constrain from VLBI observations?

10 Examples

11 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

12 Many Components in Some Jets Lister et al. 2009

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14 Multi-Epoch Stacked Images: 3C273

15 Multi-Epoch Stacked Images:

16 Distribution of Jet Opening Angles Pushkarev et al 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.

17 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

18 MOJAVE: Quasar (NRAO 140) z = pc Apparent Speed = 12.8c (Lister et al. 2009)

19 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?

20 Faraday Rotation Zavala & Taylor 2001

21 Rotation Measure Gradients 3C 273 Asada et al Multiple Scales and Epochs: Zavala & Taylor 2005; Attridge et al with mm VLBI; Asada et al. 2008

22 MOJAVE Multi-band observations: 8.1, 8.4, 12.1, 15.3 GHz Hovatta et al., in prep.

23 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

24 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 A in 3C303 by Kronberg et al (astro-ph )

25 MOJAVE: Quasar (NRAO 140) z = Circular Polarization 20 pc

26 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

27 Core Region of 3C279

28 Polarization Model of Components 5 and 4

29 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 x G cm 2 Jet is dynamically dominated by protons.

30 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

31 Summary (part 2) Polarization Studies of Parsec-Scale Jets B-fields likely dominated by tangled magnetic fields which are shocked/sheared hydrodynamically 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

32 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)