Pottschmidt, K. High Energy Astrophysics, MPI for Extraterrestrial Physics, Max Planck Society;
Gleissner, T., Wilms, J., Pottschmidt, K., Uttley, P., Nowak, M. A., & Staubert, R. (2004). Long term variability of Cyg X-1. II. The rms-flux relation. Astronomy & Astrophysics, 414(3), 1091-1104. doi:10.1051/0004-6361:20031684.