Ten new BL lacertae objects discovered by an efficient X-ray/radio/optical technique

We report the recent discovery of 10 BL Lac objects in the Einstein IPC Slew Survey by means of X-ray/ radio versus X-ray/optical color-color diagrams and confirming optical spectroscopy. These 10 BL Lac objects were discovered using a technique proposed by Stocke et al. which exploits the characteristic broad-band spectra of BL Lac objects. New VLA detections provide accurate fluxes [limiting f(6 cm) ∼ 0.5 mJy] and ∼1″ positions, facilitating the determination of an optical counterpart. All 10 new BL Lac objects show essentially featureless optical spectra and lie within the range of radio/X-ray/optical colors of known X-ray-selected BL Lac objects, when ∼1 mag optical variability is included. We expect ∼50 new BL Lac objects in total, from complete optical follow-up of our now completed VLA work and recent Australia Telescope observations, yielding a complete Slew Survey sample of ∼90 BL Lac objects.