Rapid spectral transition of the black hole binary V404 Cygni J. J. E. Kajava, C. Sánchez-Fernández, J. Alfonso-Garzón, S. E. Motta and A. Veledina A&A, 634 (2020) A94 Published online: 13 February 2020 DOI: 10.1051/0004-6361/201937191