Intermediate BL Lac objects

The 200-mJy sample, defined by Marcha et al., contains about 60 nearby, nor thern, flat-spectrum radio sources. In particular, the sample has proved ef fective at finding nearby radio-selected BL Lac objects with radio luminosi ties comparable to those of X-ray-selected objects, and low-luminosity flat -spectrum weak emission-line radio galaxies (WLRGs). The 200-mJy sample con tains 23 BL Lac objects (including 6 BL Lac candidates) and 19 WLRGs. We wi ll refer to these subsamples as the 200-mJy BL Lac sample and the 200-mJy W LRG sample, respectively. We have started a systematic analysis of the morp hological pc-scale properties of the 200-mJy radio sources using VLBI obser vations. This paper presents VLBI observations at 5 and 1.6 GHz of 14 BL Lac objects and WLRGs selected from the 200-mJy sample. The pc-scale morphology of the se objects is briefly discussed. We derive the radio beaming parameters of the 200-mJy BL Lac objects and WLRGs and compare them with those of other B L Lac samples and with a sample of FR I radio galaxies. The overall broad-b and radio, optical and X-ray properties of the 200-mJy BL Lac sample are di scussed and compared with those of other BL Lac samples, radio- and X-ray-s elected. We find that the 200-mJy BL Lac objects fill the gap between HBL a nd LBL objects in the colour-colour plot, and have intermediate alpha (XOX) as expected in the spectral energy distribution unification scenario. Fina lly, we briefly discuss the role of the WLRGs.