1ES 1741+196: a BL Lacertae object in a triplet of interacting galaxies?

We present subarcsecond resolution imaging and spectroscopy of the BL Lac object {1ES 1741+196} and neighboring galaxies. Based on 2-dimensional modelling, the host galaxy of {1ES 1741+196} is a very bright and large elliptical galaxy ({M_R} = -24.85, {r_e} = 51.2 kpc) whose overall luminosity distribution deviates significantly from a de Vaucouleurs profile. It is one of the most luminous and largest BL Lac host galaxies known. Closeby to {1ES 1741+196} we found two companion galaxies at the same redshift as the BL Lac itself. They are at projected distances of 7.2 and 25.2 kpc, respectively. The closer companion galaxy can be best modelled by a Sa-type galaxy, whereas the more distant companion galaxy is an elliptical. This is supported by their spectra. We detected a tidal tail emerging from the closer companion galaxy which is possibly connected with the more distant galaxy. Its surface brightness increases towards the closer companion galaxy, which suggests that material has been released from that galaxy due to tidal forces. The flat luminosity profile (beta = 0.15), high ellipticity (epsilon = 0.35) of the host galaxy of {1ES 1741+196} as well as its position angle along the impact parameter to the neighboring galaxies can be the result of tidal interaction. {1ES 1741+196} may be a BL Lac object in a triplet of interacting galaxies. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma, jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Institute de Astrofisica de Canarias. Based on observations collected at the German-Spanish Astronomical Centre, Calar Alto, operated by the Max-Planck-Institut für Astronomie, Heidelberg, jointly with the Spanish National Commission for Astronomy