Discovery of non-metastable ammonia masers in Sagittarius B2 Y. T. Yan, C. Henkel, K. M. Menten, Y. Gong, H. Nguyen, J. Ott, A. Ginsburg, T. L. Wilson, A. Brunthaler, A. Belloche et al. (3 more) A&A, 666 (2022) L15 Published online: 19 October 2022 DOI: 10.1051/0004-6361/202245024