Voges, W. High Energy Astrophysics, MPI for Extraterrestrial Physics, Max Planck Society;
Mickaelian, A. M., Hovhannisyan, L. R., Engels, D., Hagen, H.-J., & Voges, W. (2006). Optical identification of ROSAT-FSC sources. Astronomy & Astrophysics, 449(1), 425-433. doi:10.1051/0004-6361:20053967.