Observations of the extreme-ultraviolet transient RE J1255+266: a short outburst of a WZ Sge system?

We present a previously unpublished ROSAT Wide Field Camera observation of the transient source RE J1255+266 made just 4 d before the discovery observations. The source is not detected, limiting the duration of the outburst to be less than expected for a superoutburst of a WZ Sge system.We also present a marginal detection of X-ray emission from RE J1255+266 using ASCA. The most probable luminosity is 6x10(29) erg s(-1), which is very similar to WZ Sge itself.We discuss the nature of the source in the light of these observations, and conclude that it is most probably a WZ Sge system, but that the observed outburst must have been a normal dwarf nova outburst.