On the X-ray properties of V Sge and its relation to the supersoft X-ray binaries

We investigate the ROSAT X-ray properties of V Sge, which has been proposed to be related to supersoft X-ray binaries. During optical bright states, V Sge is a faint hard X-ray source, while during optical faint states (V >=12 mag), V Sge is a `supersoft' X-ray source. Spectral fitting confirms that V~Sge's X-ray properties during its soft X-ray state may be similar to those of supersoft X-ray binaries, although a much lower luminosity cannot be excluded. It is possible to explain the different optical/X-ray states by a variable amount of extended uneclipsed matter, which during the optical bright states contributes significantly to the optical flux and completely absorbes the soft X-ray component. An additional, perhaps permanent, hard X-ray component, such as a bremsstrahlung component with a 0.1-2.4 keV luminosity of ~10^30 erg/s, must be present to explain the X-ray properties during the optical bright/hard X-ray state.