Apparent Speed as a Probe of ParsecScale Jet in AGN

1
Apparent Speed as a Probe of Parsec-Scale Jet in
AGN

• S. Jorstad / Boston U., USA
• /St. Petersburg State U.,
  Russia
• Marscher / Boston U., USA
• M. Lister / Purdue U., USA
• A. Stirling / U. of Manchester, Jodrell Bank
  Obs., UK
• T. Cawthorne / Central Lancashire U., UK
• W. Gear / Cardiff U., UK
• J.L. Gómez / IAA, Granada, Spain
• J. Stevens / Royal Observatory, UK
• P. Smith / Steward Observatory, USA
• J. Foster / U. of California, Berkeley, USA
• I. Robson / Royal Observatory, UK

2
The Sample
Quasars BL Lac Objects Radio
galaxies PKS 0420-014 3C 66A
3C 111 PKS 0528134 OJ 287
3C 120 3C 273 1803784 3C
279 1823568 PKS 1510-089 BL
Lac 3C 345 CTA 102 3C 454.3
Instruments and Wavelengths
VLBA (7 mm ) March 1998
- April 2001 17 epochs BIMA (3 mm)
April 2000 - April 2001
3-4 epochs JCMT (0.85/1.3 mm)
March 1998 - April 2001 6-11 epochs 1.5m
Steward Obs. (6500 Å) Feb. 1999 - April
2001 4-5 epochs
3
OUTLINE

• Study of apparent speed distributions in
  individual sources and
• in different group of AGNs.
• Determination of jet parameters Doppler and
  Lorentz factors,
• viewing and opening angles.
• Searching for acceleration/deceleration in the
  jets
• Analysis of the brightness temperature on parsec
  scales.

4
Imaging
www.bu.edu/blazars/multi.html
5
Modeling

• Parameters of Component
• S (mJy) - flux density
• Sp(mJy) - polarized flux density
• R (mas) - distance from the core
• (deg) - PA relative to the core
• EVPA(deg) - electric vector PA
• a (mas) - size

www.bu.edu/blazars/multi.html
6
Classification of Components Motion
We determine the apparent speeds, ?app, for 109
knots. Superluminal apparent speeds occur in 82
of the knots. Statistically significant deviation
from ballistic motion is observed in 22 of
superluminal knots.
7
Acceleration of the Jet Flow
The majority of non-ballistic components undergo
an increase of apparent speed with distance from
the core. This could be the result of physical
accelerations (Vlahakis Königl 2004, ApJ, 605,
656) or from selection of sources whose angles to
the line of sight lt sin -1(1/?) near the core and
closer to this value farther out.
8
Light Curves of Jet Components
dt
Time Scale of Variability Burbidge, Jones,
ODell 1974, ApJ , 193, 43 ?tvar
dt/ln(Smax/Smin) Variability Doppler Factor ?var
aD/c ?tvar (1z) D - luminosity distance a -
VLBI size of component c - speed of light z -
redshift
Smax
Smin
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Flux Variability Time Scale vs. Size Variability
Time Scale
The straight line indicates The expected
relation between ?tvar and ?ta for adiabatic
losses for optically thin shock with ?0.7 ,
S??-? (Marscher Gear 1985, ApJ, 298, 114)
10
Apparent Speed - Doppler Factor Relation
2-cm survey (Kellermann et al. 2004)
11
Lorentz Factor and Viewing Angle of Jet
Components
The Lorentz factors of the jet flows in the
quasars and BL Lac objects range from ? 5 to
?gt30 the radio galaxies have lower Lorentz
factors and wider viewing angles than the blazars.
12
Intrinsic Brightness Temperature of Jet
Components
Tb,obs 7.5?108 Smax/a2 K Tb.int Tb,obs
(1z)1.7/?1.7 K ?0.7 S??-? Quasars
ltTb.int gt3.5?109 K BL Lacs ltTb.int gt5.5?107
K RG ltTb.int gt1.4?109 K Comparison of
these values with the equipartion brightness
temperature of the optically thick part of the
jets, Tb.int gt2-5?1010 K, implies a faster
decrease of Tb with distance down the jet, which
suggests a stronger magnetic field in the BL Lac
objects (Readhead 1994, ApJ, 426, 51).
13
Projected Half Opening Angles of Jets
Projected Opening Angle, ?p ?p tan -1 ? lt
strans slong ? tan -1 ? sogt strans R
slong R sin (?jet- ?)a/2
14
Intrinsic Half Opening Angles of Jets

• ? 1/? (Blandford Königl 1979,
• ApJ, 232, 34)
• Intrinsic Half Opening Angle, ?
• ? ?p sin lt ?ogt
• ? ?/? (rad), where ? 0.2 0.1
• ? v(Pext / Po) (Daly Marscher
• 1988, ApJ, 334, 539)
• ? 0.5 ? Pext / Po 1/4

15
Conclusions

• 1. We have measured the apparent speed of 106
  features in the inner jets of 15 AGNs.
  Superluminal apparent speeds occur in 80 of the
  knots, 26 of which show statistically
  significant deviations from ballistic motion. The
  majority of non-ballistic components undergo an
  increase of apparent speed with distance from the
  core.
• 2. We suggest a new method to define Doppler
  factor, based on the assumption that the decay in
  flux of the superluminal components is caused by
  radiative losses rather than by cooling from
  expansion, and is subject to light-travel delays.
• 3. The derived parameters of the jets indicate
  that in our sample the quasars have the highest
  Doppler factors and smallest viewing and opening
  angles, while the two radio galaxies possess
  significantly lower Doppler factors, larger
  viewing angles, and wider opening angles despite
  their blazar-like'' radio properties.
• 4. We have estimated the intrinsic brightness
  temperatures of jet components in the quasars, BL
  Lacs, and radio galaxies on parsec scales.
  Comparison of these values with the equipartition
  brightness temperature of the optically thick
  part of the jets suggests a stronger magnetic
  field in the BL Lac objects.