An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544–0639 F. Ursini, L. Bassani, F. Panessa, E. Pian, G. Bruni, A. Bazzano, N. Masetti, K. Sokolovsky and P. Ubertini A&A, 622 (2019) A116 Published online: 06 February 2019 DOI: 10.1051/0004-6361/201834662