Frequencydependent core shift Jet apex is there Jet

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Frequency-dependent core shift Jet apex is there Jet at ν 1 Jet at ν

Frequency-dependent core shift Jet apex is there Jet at ν 1 Jet at ν 2 < ν 1 The “core” of a VLBI jet is located in a region with τ ~ 1 and changes its position with the observing frequency

Core shift vectors: polar plots n n med (15. 4 -8. 1 GHz): 128

Core shift vectors: polar plots n n med (15. 4 -8. 1 GHz): 128 μas med (15. 4 -8. 4 GHz): 125 μas med (15. 4 -12. 1 GHz): 88 μas >80% sources within |θcore shift - θmed jet PA| < 45°

Magnetic field at 1 pc from jet apex Magnetic field is derived for the

Magnetic field at 1 pc from jet apex Magnetic field is derived for the sources with known • apparent speed • redshift • core shift It total 102 sources: 84 QSO and 18 BLO median BQuasar ~ 0. 9 G median BBL Lac ~ 0. 4 G Why the magnetic field at 1 pc is stronger in quasars? • more distant sources • faster jets • more massive central BHs and/or higher accretion rates? This scenario is supported by narrower intrinsic opening angles (Pushkarev et al. 2009)

Multi-frequency MOJAVE obs. n extended sample of 192 sources n 12 epochs (BL 137

Multi-frequency MOJAVE obs. n extended sample of 192 sources n 12 epochs (BL 137 A-L) during 2006 n polarimetric observations at 8. 1, 8. 4, 12. 1 and 15. 3 GHz n Papers planned RM (Hovatta et al. , submitted in AJ) ¨ Core shift (Pushkarev et al. , submitted to A&A) ¨ Spectral index (Hovatta et al. in prep. ) ¨

Core shift measurement method core shift core phase center offset image shift core shift

Core shift measurement method core shift core phase center offset image shift core shift = image shift – core phase center offset (from modelfit) (from 2 D)

Accuracy of the method: approach 2 Let’s assume: • the core shift is along

Accuracy of the method: approach 2 Let’s assume: • the core shift is along the jet • the accuracy is direction irrespective SD of transverse projections of the core shift vectors accuracy σ15. 4 -8. 1~ 50 μas, σ15. 4 -8. 4 ~ 51 μas, σ15. 4 -12. 1 ~ 35 μas

Core shift vs redshift Kendall’s tau: -0. 667 chance p: 0. 0123

Core shift vs redshift Kendall’s tau: -0. 667 chance p: 0. 0123