Unveiling the periodic variability patterns of the X-ray emission from the blazar PG 1553+113 T. Aniello, L. A. Antonelli, F. Tombesi, A. Lamastra, R. Middei, M. Perri, F. G. Saturni, A. Stamerra and F. Verrecchia A&A, 686 (2024) A300 Published online: 21 June 2024 DOI: 10.1051/0004-6361/202449515