1. The multi-wavelength polarization VLBI structure of 3 BL Lacertae objects Vladislavs Bezrukovs, Dr. Denise Gabuzda EVN 8 th Symposium 26 – 29 September, 2006 Torun, Poland University College Cork Cork Institute of technology ENIGMA, Irish team

2. Introduction Kuhr and Schmidt BL Lacerate objects sample; 1308+326 Intensity and polarization model fitting; Helical B Field in the jet? Polarization rotation in 43 GHz. 0828+493 Intensity and polarization model fitting; Helical B Field in the jet? 1803+784 Intensity and polarization model fitting; Helical B Field in the jet? RM gradient in the jet.

3. Project background My project: To analyze VLBA data from Kuhr and Schmidt sample of BL Lac objects > 1 Jy at 43 GHz, 22 GHz and 15 GHz (May 2002, August 2002, November 2004)

4. Kuhr and Schmidt sample of BL Lac objects

5. BL Lac objects properties BL Lac objects are active galactic nuclei with: relatively low-luminosity optical line emission; in many cases their optical continua are completely featureless; strong and variable polarization in wavebands ranging from optical through radio; compact, flat-spectrum radio structure; point-like optical structure; the radio emission and much of the optical emission is believed to be synchrotron radiation. the VLBI core polarizations have values ranging from ~2-7 per cent, and occasionally reaching values as high as ~10 per cent. 60–70 per cent of BL Lac objects have jets that have transverse magnetic fields. At the same time, a sizeable minority of about 30 per cent have longitudinal jet magnetic fields. (Gabuzda, Pushkarev, Cawthorne et el 1999)

6. 1308+326 (August 2002)

7. 22 GHz map Intensity (mJy) 1) 1811.0 2) 161.0 3) 163.0 4) 57.4 5) 53.7 Polarization (mJy) and EVPA (deg) 1) 57.967.08 2)1.554.37 3) 15.1 -26.23 43 GHz map Intensity (mJy) 1) 1310.0 1b) 230.5 2) 82.8 3) 113.2 Polarization (mJy) and EVPA (deg) 1) 98.633.592 15 GHz map Intensity (mJy) 1) 1510.8 2) 184.1 3) 137.0 4) 148.0 5) 44.9 Polarization (mJy) and EVPA (deg) 1) 57.996.578 2) 10.963.087 3) 18.5 -5.44 1308+326. Model fitting.

9. Spectrum in core region positive -> core optically thick Spectrum in core region negative -> core optically thin 1308+326. Spectral index maps.

10. Why we rotate polarization angle in 43 GHz to 90 o ? 1308+326. Rotation measure.

12. MOJAVE Sample 15 GHZ Intensity map with polarization sticks 1308+326. November 2002 epoch compare with MOJAVE data. MOJAVE Sample

13. 0828+493 (November 2004)

14. 43GHz map Intensity (mJy) 1) 114.2 2) 51.5 3) 103 Polarization (mJy) and EVPA (deg) 1) 4.09 89.146 22GHz map Intensity (mJy) 1) 143.6 2) 79.2 3) 100.2 Polarization (mJy) and EVPA (deg) 1) 2.2 80.06 2) 3.2116.06 15GHz map Intensity (mJy) 1) 153.4 2) 65.9 3) 134.8 Polarization (mJy) and EVPA (deg) 1) 2.3 94.132 2) 2.9121.132 3) 2.4 7.132 0828+493. Model fitting.

16. 0828+493. Rotation Measure. RM made from 15 and 22 GHz.

17. 1803+784 (May 2002)

18. 43 GHz map Intensity (mJy) 1) 1091.0 2) 146.0 3) 173.0 Polarization (mJy) and EVPA (deg) 1) 37.0129.65 2) 12.7 76.4 22 GHz map Intensity (mJy) 1) 1688.7 2) 144.5 3) 270.0 Polarization (mJy) and EVPA (deg) 1) 60.7132.87 2) 28.6 78.81 15 GHz map Intensity (mJy) 1) 1709.0 2) 174.6 3) 278.4 4) 47.9 Polarization (mJy) and EVPA (deg) 1) 57.4139.74 2) 33.9 81.74 1803+784. Model fitting.

20. 1803+784. May 2002 Epoch compare with MOJAVE data. MOJAVE Sample

21. 1803+784. Rotation measure.

22. Zavala and Taylor et. el. 2003 (epoch 2000) Mehreen Mahmud image (epoch 2003) 1803+784. Rotation measure. RM gradient change direction !!!

23. Summary. Possibility of Helical magnetic field in these sources 1308+326 : transverse magnetic field in jet; 0828+493 : longitudinal polarization in sheath; 1803+784 : asymmetric RM distribution across the jet; 1308+326 core changes from optically thick in 15 and 22 GHz to optically thin between 22 and 43 GHz; taking into account gives core rotation measure ~3500 rad/m 2 ; Produced and tested version of VISFIT program in Linux (intensity and polarization model fitting); available to all interested.

24. Acknowledgements to Dr. Denise Gabuzda, Radio Astronomy Lab at UCC, Enigma, Irish Group.