The Einstein Slew Survey sample of BL Lacertae objects

We have used an efficient method of finding new BL Lacertae objects in the Einstein Slew Survey suggested by Stocke et al. By exploiting the unique broadband (radio/optical/X-ray) spectra of X-ray-selected BL Lac objects, we have identified 29 new BL Lac objects out of 32 candidates observed, effectively doubling the size of the Slew Survey BL Lac sample, which now includes 62 objects. Six more BL Lac candidates have yet to be observed, and seven blank field radio sources cannot be ruled out as optically faint BL Lac objects, although this is unlikely. The correct classification of one BL Lac candidate remains uncertain. We present finding charts optical spectroscopy, radio images, and optical polarimetry for these new BL Lac objects. Based upon nearly complete radio imaging and optical spectroscopy observations, we present the northern, high-latitude Slew Survey BL Lac sample, in the area bounded by δ ≥ -40° and \b_II| ≥ 15° and excluding the region within 5° of M31. This sample contains 48 BL Lac objects, five BL Lac candidates, and five blank fields which may contain possible BL Lac candidates. This is considerably larger than any previous complete sample of BL Lac objects. We compare this sample with the X-ray-selected Extended Medium-Sensitivity Survey (EMSS) sample of BL Lac objects as well as the radioselected 1 Jy sample.