We report the results of our optical multicolour monitoring campaign o
f the supersoft X-ray source RXJ0513.9-6951. During this campaign, RXJ
0513.9-6951 went through an optical low-state, lasting similar to 40 d
ays. The decrease of the optical flux, Delta V similar to 1 mag, and t
he accompanying reddening, Delta(B-V) similar to 0.1-0.2 mag and simil
ar to(V-R) similar to 0.1 mag, can be quantitatively described by vari
ations in the irradiation of the accretion disk by the hot central sta
r. In this simple model, we consider a white dwarf with nuclear burnin
g of accreted matter. Its photospheric radius shrinks in response to a
temporarily slightly reduced mass-transfer rate. The same model can a
ccount for the temporarily increased soft X-ray flux observed twice wi
th ROSAT and we expect that during the optical low-state the system tu
rned on again as a soft X-ray source in the 0.1-2.4 keV energy band.