Are some BL Lac objects artefacts of gravitational lensing

BL Lac objects are extragalactic, highly variable, polarized sources with significant emission from radio to X-ray wavelengths. However, despite extensive research, their nature and origin remain unclear. The authors propose that a significant fraction of the BL Lac objects are optically violently variable quasars (OVVs) whose continuum emission has been greatly amplified, relative to the line emission, by point-like gravitational lenses in intervening galaxies. Several anomalous physical and statistical properties of BL Lacs can be understood on the basis of this model, which is immediately testable on the basis of absorption line studies and by direct imaging. (author)