J004457+4123 (Sharov 21): not a remarkable nova in M 31 but a background quasar with a spectacular UV flareH. Meusinger, M. Henze, K. Birkle, W. Pietsch, B. Williams, D. Hatzidimitriou, R. Nesci, H. Mandel, S. Ertel, A. Hinze and T. BertholdA&A, 512 (2010) A1DOI: https://doi.org/10.1051/0004-6361/200913526
