The multiwavelength polarization VLBI

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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
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Introduction

• Kuhr and Schmidt BL Lacerate objects sample
• 1308326
• Intensity and polarization model fitting
• Helical B Field in the jet?
• Polarization rotation in 43 GHz.
• 0828493
• Intensity and polarization model fitting
• Helical B Field in the jet?
• 1803784
• Intensity and polarization model fitting
• Helical B Field in the jet?
• RM gradient in the jet.

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Project background

• My project
• To analyze VLBA data from Kuhr and Schmidt
  sample of BL Lac objects gt 1 Jy at 43 GHz, 22 GHz
  and 15 GHz (May 2002, August 2002, November 2004)

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Kuhr and Schmidt sample of BL Lac objects
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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.
• 6070 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)

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1308326(August 2002)
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1308326. 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
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1308326. Model fitting.
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1308326. Spectral index maps.
Spectrum in core region positive -gt core
optically thick
Spectrum in core region negative -gt core
optically thin
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1308326. Rotation measure.
Why we rotate polarization angle in 43 GHz to 90o?
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1308326. Rotation measure.
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1308326. November 2002 epoch compare with MOJAVE
data.
15 GHZ Intensity map with polarization sticks
MOJAVE Sample
MOJAVE Sample
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0828493(November 2004)
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0828493. 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
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0828493. Model fitting.
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0828493. Rotation Measure.
RM made from 15 and 22 GHz.
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1803784(May 2002)
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1803784. 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
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1803784. Model fitting.
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1803784. May 2002 Epoch compare with MOJAVE
data.
MOJAVE Sample
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1803784. Rotation measure.
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1803784. Rotation measure.
RM gradient change direction !!!
Zavala and Taylor et. el. 2003 (epoch 2000)
Mehreen Mahmud image (epoch 2003)
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Summary.

• Possibility of Helical magnetic field in these
  sources
• 1308326 transverse magnetic field in jet
• 0828493 longitudinal polarization in sheath
• 1803784 asymmetric RM distribution across the
  jet
• 1308326 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.

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