MultiFrequency Polarization Properties of Blazars S Jorstad Boston

Multi-Frequency Polarization Properties of Blazars S. Jorstad / Boston U. , USA A. Marscher / Boston U. , USA J. Stevens / Royal Observatory, Edinburgh, UK A. Stirling / Royal Observatory, Edinburgh, UK M. Lister / Purdue U. , USA P. Smith / Steward Obs. , U. of Arizona, USA T. Cawthorne / U. Central Lancashire, UK J. L. Gómez / IAA, Granada, Spain D. Gabuzda / U. College Cork, Ireland W. Gear / Cardiff U. , UK I. Robson / Royal Observatory, Edinburgh, UK

The Sample Quasars BL Lac Objects PKS 0420 -014 3 C 66 A PKS 0528+134 OJ 287 3 C 273 1803+784 3 C 279 1823+568 PKS 1510 -089 BL Lac 3 C 345 CTA 102 3 C 454. 3 Radio galaxies 3 C 111 3 C 120 Instruments and Wavelengths VLBA (7 mm ) BIMA (3 mm) JCMT (0. 85/1. 3 mm) 1. 5 m Steward Obs. (~6500 Å) March 1998 April 2000 March 1998 Feb. 1999 - April 2001 17 epochs April 2001 3 -4 epochs April 2001 6 -11 epochs April 2005 4 -5 epochs

Imaging www. bu. edu/blazars/multi. html

Goals Of the Project 1. To investigate connection between the polarized mm, sub-mm, and optical emission and structure of the radio jets. 2. To define time scales of variability of the polarization parameters at different frequencies. 3. To search for relation between variability of the polarization parameters and dynamical processes in the jets. 4. To determine parameters of the jets (apparent speed, acceleration/deceleration of the jet flow, viewing and opening angles, ejection rate).

Apparent Speed of Jet Components 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.

Light Curves of Jet Components dt Time Scale of Variability Burbidge, Jones, & O’Dell 1974, Ap. J , 193, 43 tvar = dt/ln(Smax/Smin) Smax Smin Variability Doppler Factor var = a. D/[c tvar (1+z)] D - luminosity distance a - VLBI size of component c - speed of light z - redshift

Lorentz Factor and Viewing Angle of Jets The Lorentz factors of the jet flows in the quasars and BL Lac objects range from ~ 5 to >30; the radio galaxies have lower Lorentz factors and wider viewing angles than the blazars (Jorstad et al. 2005, submitted to AJ).

Group I (“BLLac-like”): 3 C 66 A, 3 C 279, 3 C 345, 1803+784, 1823+568, and BL Lac); the EVPA at most epochs is roughly parallel to the jet axis at different frequencies

1823+568

Group II (“Quasar-like”): 0420 -014, 0528+134, OJ 287, 1510 -089, CTA 102, and 3 C 454. 3; EVPA in the VLBI core is variable but at many epochs 43 GHz core, 230 GHz, and optical electric vector position angle correspond to each other.

0528+134

Group III (“unpolarized VLBI core”): 3 C 111, 3 C 120, and 3 C 273; the JCMT polarization is similar to the 43 GHz polarization of a very strong superluminal component.

Group III Connection between maximum fractional polarization at 7 mm (core), 1 mm, and in the optical region Consider the highest state of polarization for each source: Separation into groups is supported by different values of fractional polarization: 1. Group I objects show the highest polarization at all wavelengths: from 7% to 25 % at 7 mm, from 10% to 36% at 1 mm, and from 8% to 40% in the optical region. 2. Group II objects possess similar polarization at 7 and 1 mm (~ 8%). 3. Objects with unpolarized VLBI core have the lowest level of optical polarization.

Group III Connection between minimum fractional polarization at 7 mm (core), 1 mm, and in the optical region For the lowest state of polarization of each source: Separation into groups is supported by different values of fractional polarization: 1. Group I objects show the highest polarization at all wavelengths. 2. Group II objects possess similar polarization at 7 and 1 mm (~ 1 -2%). 3. Objects with unpolarized VLBI core have the lowest level of the polarization at all wavelengths.

Group III Difference between EVPA during high and low polarization states Group II objects show significant scatter between EVPAs during the high and low polarization states, while Group I objects have only a small difference in polarization direction (within 20 o) between the states.

Connection between polarization level and disturbances in the jet flow

Conclusions 1. Analysis of the data shows an obvious connection between the polarized 2. emission at sub-mm wavelengths and strongest polarized emission in parsec-scale 3. jets of the quasars and BL Lac objects. This implies co-spatiality of the emission 4. region or roughly the same magnetic field direction in the emission regions at 5. both frequencies. 6. 2. The sample demonstrates a significant correlation between fractional polarization 7. in the optical region and level of polarization of the VLBI core (Lister & Smith 2000) 8. 3. For the “quasar –like “ group of sources there is a connection between increases 9. in the fractional polarization of the VLBI core, sub-mm and optical polarization 10. and ejections of new superluminal knots. This suggests that high levels of 11. polarization in these objects result from ordering of the magnetic field by 12. shock formation (Marscher & Gear 1985) which is responsible for the polarized 13. emission at different wavelength. 14. 4. The “BL Lac-like” group of sources contains the highest fractional polarization 15. and most stable direction of polarization along the jet. This is possible to explain 16. for jets with intrinsic toroidal magnetic field ( in the frame of the jet) that is of the 17. order of, or stronger than, the intrinsic poloidal field. In this case, the highly relativist 18. motion implies that, in the observer’s frame, the jet is strongly dominated by the 19. toroidal magnetic field B /Bll >Γ (Lyutikov et al. 2005).