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K. C. Peterson (Yale University), T. A. Rector (NRAO, Socorro), D. C. Gabuzda (University College Cork, Ireland)
In the standard unified model, BL Lacs are believed to be low-luminosity FR-1 radio galaxies viewed at small angles to their jet axes. However, the relationship between high-energy peaked BL Lacs (HBLs) and low-energy peaked BL Lacs (LBLs) is still unclear. Studying BL Lacs with VLBI techniques is promising because the properties of their parsec-scale jets are strongly dependent on the orientation and Lorentz factor of the jet. Due to their relative radio-faintness, HBLs have not been as well studied on VLBI scales as LBLs. We present results of a 2-epoch VLBI survey of 12 HBLs, the first search for proper motion in the parsec-scale radio jets of HBLs. Based on the measured positions of jet components in two epochs, velocities are consistent with no motion, but we are able to place upper limits of approximately 2c on the apparent motions. We present these results and their implications for the HBL jet orientation angles and Lorentz factors, important parameters in BL Lac unification models. This research was carried out as part of the NSF's Research Experience for Undergraduates (REU) program at the NRAO in Socorro, New Mexico.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.