Multi-Frequency Polarization Properties of Blazars

1. 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

2. The Sample Quasars BL Lac Objects Radio galaxies PKS 0420-014 3C 66A 3C 111 PKS 0528+134 OJ 287 3C 120 3C 273 1803+784 3C 279 1823+568 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 2005 4-5 epochs

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

5. Goals Of the Project • 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).

6. 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.

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

8. 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).

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

10. 1823+568

11. Group II (“Quasar-like”): 0420-014, 0528+134, OJ 287, 1510-089, CTA102, and 3C454.3; 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.

12. 0528+134

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

14. Group I Group II Group III Connection between maximum fractional polarization at 7mm (core), 1mm, 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 7mm, • from 10% to 36% at 1mm, and from 8% to 40% • in the optical region. • 2. Group II objects possess similar polarization • at 7 and 1mm (~ 8%). • 3. Objects with unpolarized VLBI core have • the lowest level of optical polarization.

15. Group I Group II Group III Connection between minimum fractional polarization at 7mm (core), 1mm, 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 1mm (~ 1-2%). • 3. Objects with unpolarized VLBI core have • the lowest level of the polarization at all • wavelengths.

16. Group I Group II 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 20o) between the states.

17. Connection between polarization level and disturbances in the jet flow

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