High-resolution imaging of Einstein Slew Survey BL lacertae objects

High-resolution images of 7 newly identified BL Lac objects (among them one BL Lac candidate) at z less than or equal to 0.2 from the Einstein Slew Su rvey are presented for the first time. In all cases we were able to resolve the host galaxy. Our a-dimensional analysis of the host galaxies shows tha t all these BL Lac objects are embedded in elliptical galaxies with an aver age M-R = -23.1 and r(e) = 10 kpc. One BL Lac might have both a bulge and a n underlying disk. These results are similar to those obtained for the host s of other BL Lac objects. We searched in our BL Lac objects for host galaxies, whose surface brightne ss distribution does not follow a pure de Vaucouleurs law and determined th e statistical significance with numerical simulations. In two BL Lac object s (1ES 1255+244 and 1ES 1959+650) significant deviations were found. The environments of the BL Lac objects are highly interesting. In at least two (perhaps three) cases we found evidence for interaction. All BL Lac obj ects (except one) have at least 2 companions, some of which are bright, wit hin a projected distance of 60 kpc from the BL Lac. In two cases we found 5 companions within 50 kpc. This implies that gravitational interaction is p otentially important to the BL Lac phenomenon at least in these sources.