Long-term variability of AGN at hard X-raysS. Soldi, V. Beckmann, W. H. Baumgartner, G. Ponti, C. R. Shrader, P. Lubiński, H. A. Krimm, F. Mattana and J. TuellerA&A, 563 (2014) A57DOI: https://doi.org/10.1051/0004-6361/201322653
