We present first-epoch VLBA observations obtained as part of a program to study the parsec-scale radio structure of a sample of twelve X-ray-selected BL Lacs (XBLs) chosen to span the observed range of spectral energy distributions for XBLs. Whereas radio-selected BL Lacs (RBLs) show a bimodal distribution of parsec- and kpc-scale jet alignment angles, all of the XBLs that are resolved on poth parsec- and kpc-scales have well-aligned jets. This can be interpreted as support for orientation models in which XBLs are believed to be seen further off-axis than RBLs. Alternatively, XBL jets may be intrinsically straighter than those found in RBLs. This may be due, perhaps, to their intrinsically lower power levels.
American Astronomical Society Meeting Abstracts #194
- Pub Date:
- May 1999