Freyberg, M. J. High Energy Astrophysics, MPI for Extraterrestrial Physics, Max Planck Society;
Costantini, E., Pinto, C., Kaastra, J. S., in’t Zand, J. J. M., Freyberg, M. J., Kuiper, L., et al. (2012). XMM-Newton observation of 4U 1820-30 - broad band spectrum and the contribution of the cold interstellar medium. Astronomy & Astrophysics, 539: A32, pp. 1-13. doi:10.1051/0004-6361/201117818.