The light curve below of RXJ0558.3+6753 was obtained on the night of September 13/14, 2002 at CBA Belgium Observatory, using our regular equipment (0.35-m f/6.3 SCT and unfiltered ST-7 CCD), under very good sky conditions. No obvious large-amplitude modulations are seen. 

Two nights later (Sep 15/16, 2002), I had another CCD photometry session under excellent sky conditions. The variable was observed for over 4.6 hours. Compared to my Sep 13/14 observations, the variable had faded by 1.0 mag.

Contrary to the Sep 13/14 observations, the resulting light curve of RXJ0558.3+6753 this time shows obvious large amplitude modulations, up to 0.4 - 0.5 mag (see below). Although a visual inspection of the light curve seems to indicate some periodicity in the signal, this is not directly confirmed by any of the period analysis programmes I'm using.

The variable very likely is on its way back to quiescence, but I would like to ask all observers to keep a close eye on this object for possible rebrightenings, and future outbursts. It is clear that the determination of the true nature of RXJ0558.3+6753 will require intensive follow-up observations.

After publication of my observations on VSNET, the following comments were received from John R. Thorstensen, Professor of Physics at Dartmouth College :