Relativistic supernova 2009bb exploded close to an atomic gas cloud M. J. Michałowski, G. Gentile, T. Krühler, H. Kuncarayakti, P. Kamphuis, J. Hjorth, S. Berta, V. D’Elia, J. Elliott, L. Galbany et al. (12 more) A&A, 618 (2018) A104 Published online: 22 October 2018 DOI: 10.1051/0004-6361/201732356