Multiband optical polarimetry of BL Lacertae objects with the Nordic Optical Telescope L. Tommasi, E. Palazzi, E. Pian, V. Piirola, E. Poretti, F. Scaltriti, A. Sillanpää, L. Takalo and A. Treves A&A, 376 1 (2001) 51-58 Published online: 15 September 2001 DOI: 10.1051/0004-6361:20010940