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We present 88 multi-epoch Very Long Baseline Array (VLBA) images (most at anobserving frequency of 8 GHz), of 20 TeV blazars, all of the HBL class, thathave not been previously studied at multiple epochs on the parsec scale. Fromthese 20 sources, we analyze the apparent speeds of 43 jet components that areall detected at four or more epochs. As has been found for other TeV HBLs, theapparent speeds of these components are relatively slow. About two-thirds ofthe components have an apparent speed that is consistent (within two-sigma)with no motion; and some of these components may be stationary patterns whoseapparent speed does not relate to the underlying bulk flow speed. In addition,a superluminal tail to the apparent speed distribution of the TeV HBLs isdetected for the first time, with eight components in seven sources having atwo-sigma lower limit on the apparent speed exceeding 1c. We combine the datafrom these 20 sources with an additional 18 sources from the literature toanalyze the complete apparent speed distribution of all 38 TeV HBLs that havebeen studied with VLBI at multiple epochs. The highest two-sigma apparent speedlower limit considering all sources is 3.6c. This suggests that bulk Lorentzfactors of up to about 4, but probably not much higher, exist in theparsec-scale radio emitting regions of these sources, consistent with estimatesobtained in the radio by other means such as brightness temperatures. This canbe reconciled with the high Lorentz factors estimated from the high-energy dataif the jet has velocity structures consisting of different emission regionswith different Lorentz factors. In particular, we analyze the current apparentspeed data for the TeV HBLs in the context of a model with a fast central spineand a slower outer layer.

Multi-Epoch VLBA Imaging of Twenty New TeV Blazars: Apparent Jet Speeds