Radio constraints on relativistic beaming models of BL lacertae objects

We present new deep radio images of seven X-ray-selected BL Lacertae objects (XBLs) completing our survey of XBLs detected by HEAO 1. The diffuse, extended radio structures of XBLs have extended radio luminosities in the range of 10(23)-10(25) W Hz(-1). These radio measurements are compared with similar data for radio-selected BL Lacertae objects (RBLs) and galaxies. All three classes have parallel correlations between the radio luminosity of the core and extended radio luminosities with P-ext proportional to P-core(1.2). The cores of the XBLs and RBLs are on average 160 and 4000 times (respectively) stronger than the galaxy cores when normalized to a constant extended radio luminosity. This result is consistent with the expectations of unified schemes connecting BL Lacertae objects and radio galaxies via different jet orientations. The high level of core enhancement in BL Lacertae objects is incompatible with simple models assuming a continuous jet requiring jets with a few discrete components. Assuming a constant jet Lorentz factor Gamma, the core enhancements require that Gamma > 4.5 and probably exceed Gamma = 6, with average angles to the line of sight of approximately 60 degrees, 20 degrees, and 10 degrees for the galaxies, XBLs, and RBLs (respectively). These results are consistent with independent estimates from studies of BL Lacertae objects' superluminal speeds and luminosity functions.