Discovery of four gravitational lensing systems by clusters in the SDSS DR6

We report the discovery of 4 new strong lensing systems by visual inspection of the Sloan Digital Sky Survey images of galaxy clusters in Data Release 6 (SDSS DR6). Two of them show Einstein rings, and the others show tangential giant arcs. These arcs or rings have large angle separations (>8'') from the bright central galaxies and show blue color compared to the red cluster galaxies. In addition, we also found 4 probable and 4 possible lenses by galaxy clusters.