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

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

Vladislavs Bezrukovs,Dr. Denise Gabuzda

EVN 8th Symposium26 – 29 September, 2006

Torun, Poland

University College CorkCork Institute of technologyENIGMA,Irish team

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.

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)

BG121A May 2002

BG121B August 2002

BG121C November 2004

0003-006 0119+115 0814+453 0235+164 0454+844 0828+493 0745+241 0954+658 0851+202 1147+245 1308+326 1334+127 1803+784 1749+096 1807-698 2155-152 2007+777

In 1990, Kuhr and Schmidt compiled a complete sample of radio-bright BL Lac objects in the Northern sky, consisting 34 sources satisfying the following selection criteria: 1) total flux at 5 GHz I 1 Jy at the epoch at which the sample was compiled; 2) two-point spectral index between 11 and 6 cm )~(5.0611

Sa ;

3) equivalent width of emission lines Wo

A5 . The sample included sources brighter than 20m in the optical with declination 20 located outside the Galactic plane (|b|>10o).

0003-06 0454+84 0823+03 1334-12 1749+70 2150+17 0048-09 0716+71 0828+49 1418+54 1803+78 2155-15 0119+11 0735+17 0851+20 1538+14 1807+69 2200+42 0138-09 0745+24 0954+65 1652+39 1823+56 2254+07 0235+16 0814+42 1147+24 1732+38 2007+77 0256+07 0820+22 1308+32 1749+09 2131-02

Kuhr and Schmidt sample of BL Lac objects

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)

1308+326(August 2002)

22 GHz mapIntensity (mJy) 1) 1811.02) 161.03) 163.04) 57.45) 53.7

Polarization (mJy)and EVPA (deg)1) 57.9 67.082) 1.5 54.373) 15.1 -26.23

43 GHz mapIntensity (mJy) 1) 1310.01b) 230.52) 82.83) 113.2

Polarization (mJy)and EVPA (deg)1) 98.6 33.592

15 GHz mapIntensity (mJy) 1) 1510.82) 184.13) 137.04) 148.05) 44.9

Polarization (mJy)and EVPA (deg)1) 57.9 96.5782) 10.9 63.0873) 18.5 -5.44

1308+326. Model fitting.

Spectrum in core region positive ->core optically thick

Spectrum in core region negative ->core optically thin

1308+326. Spectral index maps.

Why we rotate polarization angle in 43 GHz to 90o?

1308+326. Rotation measure.

MOJAVE Sample

15 GHZ Intensity map with polarization sticks

1308+326. November 2002 epoch compare with MOJAVE data.

MOJAVE Sample

0828+493(November 2004)

43GHz mapIntensity (mJy) 1) 114.22) 51.53) 103

Polarization (mJy)and EVPA (deg)1) 4.09 89.146

22GHz mapIntensity (mJy) 1) 143.62) 79.23) 100.2

Polarization (mJy)and EVPA (deg)1) 2.2 80.062) 3.2 116.06

15GHz mapIntensity (mJy) 1) 153.42) 65.93) 134.8

Polarization (mJy) and EVPA (deg)1) 2.3 94.1322) 2.9 121.1323) 2.4 7.132


0828+493. Rotation Measure.

RM made from 15 and 22 GHz.

1803+784(May 2002)

43 GHz mapIntensity (mJy) 1) 1091.02) 146.03) 173.0


22 GHz mapIntensity (mJy) 1) 1688.72) 144.53) 270.0


15 GHz mapIntensity (mJy) 1) 1709.02) 174.63) 278.44) 47.9



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

MOJAVE Sample

Zavala and Taylor et. el. 2003(epoch 2000)

Mehreen Mahmud image(epoch 2003)

1803+784. Rotation measure.RM gradient change direction !!!

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.

Acknowledgements to

Dr. Denise Gabuzda,

Radio Astronomy Lab at UCC,

Enigma, Irish Group.

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

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