Giovannini, Gabriele

Exploring the parsec scale properties of BL Lac sources.

Author list: G. Giovannini, E. Liuzzo, M. Giroletti, B. Boccardi, S. Tamburri, C. Casadio

BL Lac objects are the most abundant emitters in gamma-ray band. However most of them are relatively low power radio sources even if the presence of relativistic jets is expected from unification models and observed properties. To increase our knowledge on parsec scale properties of BL Lacs we selected a homogeneous sample of BL Lac sources with no constrain on their radio and gamma-ray emission. We present here new VLBA observations at 8 and 22 GHz for this sample and discuss the presence of relativistic jets, in comparison with nuclear properties of radio galaxies. A comparison with gamma-ray properties will be also shortly presented.