Distortion Effects in BL Lac Radio Jets

  • H. Sol
  • S. Appl
  • L. Vicente
Conference paper
Part of the International Astronomical Union book series (IAUS, volume 175)


BL Lac objects often show a quite distorted radio morphology. Almost 75% of the BL Lacs for which the information is available show an apparent misalignment angle ΔPA between the VLBI jet and the large scale radio structure larger than 45 degrees. This can be explained by strong enhancement of slight bending due to projection effects, especially if BL Lacs are the most highly beamed sources. However we recently performed a statistical analysis of misalignment angle histograms for 155 extragalactic radio sources of different types and found that the intrinsic distortion is significantly more important in BL Lacs than in quasars and even CSS sources. Indeed the best fits of the ΔPA histograms by a simple bend model correspond to γψ = 123° for BL Lacs, 37° for quasars and 36° for CSS sources, where ψ and γ are the jet typical intrinsic bend and Lorentz factor within a given class of sources (Appl et al, 1995). If, as currently thought, jets in BL Lacs have smaller Lorentz factors than in quasars, high intrinsic bending and misalignment appear to be the rule in BL Lac sources.


Black Hole Accretion Disc Misalignment Angle Central Black Hole Ambient Magnetic Field 
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Copyright information

© International Astronomical Union 1996

Authors and Affiliations

  • H. Sol
    • 1
  • S. Appl
    • 2
  • L. Vicente
    • 1
  1. 1.Observatoire de Paris-MeudonDARC, UPR176 du CNRSFrance
  2. 2.Observatoire Astronomique11 rue de l’UniversitéStrasbourgFrance

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