1997A&A...323L..41V

We present optical CCD photometry of the supersoft X-ray source RX J0439.8-6809. The absence of significant X-ray and optical variability (3σ peak-to-peak {DELTA}V<0.07) and the optical faintness (V∼21.6) put severe constraints on a possible binary nature. Without rather unusual assumptions, a main-sequence donor star seems to be ruled out. All of the available information suggests that RX J0439 is either a double-degenerate supersoft X-ray source with a predicted orbital period of a few minutes or an extremely hot single pre-white dwarf. In either case, it is an extraordinarily rare and interesting object.