Discovery of a galactic supersoft binary X-ray source.
Burwitz, V.; Beuermann, K.; de Martino, D.; Pakull, M. W.; Truemper, J.; Robinson, E. L.; Zhang, E.; Schwope, A. D.; Thomas, H. -C.; Reinsch, K.; Barwig, H.; van Teeseling, A.; Mantel, K. -H.
Abstract
We report the discovery of the galactic very soft ('supersoft') X-ray source RXJ0019.8+2156 and its 12.2mag optical counterpart. The system displays quasi-sinusoidal modulations of the optical, UV, and X-ray light curves as well as regular radial-velocity variations with a 15.85 hour period which we interpret as the binary orbital period. The system shows little long-term variability (1990-1993) in the optical, W, and X-ray bands. The hot component may be a white dwarf which accretes at a rate of ~10^-7^Msun_/yr near the limit of stable burning of hydrogen. The system may currently be in a low state between weak shell flashes.