  In a recent ROSAT observation, taken during its optical low state, we found
that the VY Scl star V751 Cyg was a highly luminous source of soft X-rays. The
ROSAT HRI count rate of V751 Cyg was a factor of 10-20 higher than upper limits
obtained with ROSAT during previous observations, during which V751 Cyg
happened to be in the optical high state. Analysis of the X-ray spectrum
suggests a very low temperature (kT~15 eV) and a bolometric luminosity of
5*10^36 (D/500 pc)^2 erg/s. These values are characteristic of supersoft X-ray
sources. Based on the supersoft nature of V751 Cyg and the similarity of the
variability pattern of VY Scl stars and the supersoft transient source RX
J0513.9-6951 we hypothezise a relation between VY Scl stars and supersoft X-ray
sources. It is conceivable that VY Scl stars are all supersoft binaries (SSB),
that they form an extension of the previously known class of SSBs towards lower
white dwarf masses and lower temperatures.
