An ultraluminous supersoft source with a 4 hour modulation in NGC 4631 S. Carpano, A. M. T. Pollock, A. R. King, J. Wilms and M. Ehle A&A, 471 3 (2007) L55-L58 Published online: 09 July 2007 DOI: 10.1051/0004-6361:20077605