An extremely X-ray weak blazar at z = 5 S. Belladitta, A. Moretti, A. Caccianiga, G. Ghisellini, C. Cicone, T. Sbarrato, L. Ighina and M. Pedani A&A, 629 (2019) A68 Published online: 06 September 2019 DOI: 10.1051/0004-6361/201935965