Revealing the structure of the lensed quasar Q 0957+561 - I. Accretion disk size C. Fian, E. Mediavilla, J. Jiménez-Vicente, V. Motta, J. A. Muñoz, D. Chelouche, P. Goméz-Alvarez, K. Rojas and A. Hanslmeier A&A, 654 (2021) A70 Published online: 12 October 2021 DOI: 10.1051/0004-6361/202039854