Extended radio emission in BL Lac objects - I. The images

We have observed 28 sources selected from the 1Jy sample of BC Lac objects (Stickel et al. 1991) with the Very Large Array (VLA) in A, B and D configu rations at 1.36, 1.66 and 4.85 GHz, and/or with the Westerbork Synthesis Ra dio Telescope (WSRT) at 1.40 GHz. In this paper we present high sensitivity images at arcsecond resolution of the 18 objects showing extended structur e in our images, and of another source from the FIRST (Faint Images of the Radio Sky at Twenty-cm) survey (Becker et al. 1995). In general our high se nsitivity images reveal an amount of extended emission larger than previous ly reported. In some objects the luminosity of the extended structure is co mparable with that of FR II radio sources. A future paper will be devoted t o the interpretation of these results.