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The multi-wavelength polarization VLBI structure of 3 BL Lacertae objects Vladislavs Bezrukovs,

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

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The multi-wavelength polarization VLBI structure of 3 BL Lacertae objects Vladislavs Bezrukovs,

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  1. EVN 8th Symposium 26 – 29 September, 2006 Torun, Poland The multi-wavelength polarization VLBI structure of 3 BL Lacertae objects Vladislavs Bezrukovs, Dr. Denise Gabuzda 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. 1308+326. Model fitting. • 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) 57.9 67.08 • 1.5 54.37 • 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) 98.6 33.592 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) 57.9 96.578 2) 10.9 63.087 3) 18.5 -5.44

  8. 1308+326. Model fitting.

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

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

  11. 1308+326. Rotation measure.

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

  13. 0828+493(November 2004)

  14. 0828+493. Model fitting. 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) 3.2 116.06 15GHz map Intensity (mJy) 1) 153.4 2) 65.9 3) 134.8 Polarization (mJy) and EVPA (deg) 1) 2.3 94.132 2) 2.9 121.132 3) 2.4 7.132

  15. 0828+493. Model fitting.

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

  17. 1803+784(May 2002)

  18. 1803+784. Model fitting. 43 GHz map Intensity (mJy) 1) 1091.0 2) 146.0 3) 173.0 Polarization (mJy) and EVPA (deg) 1) 37.0 129.65 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) 60.7 132.87 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) 57.4 139.74 2) 33.9 81.74

  19. 1803+784. Model fitting.

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

  21. 1803+784. Rotation measure.

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

  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/m2; • 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.

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