  We test whether the model proposed by Esin et al. to explain X-ray
observations of the black hole soft X-ray transient GRS 1124-68 in outburst can
also explain the optical lightcurves of a similar object A0620-00. We show that
to reproduce the observed X-ray to optical flux ratio in A0620-00, we need to
assume X-ray irradiation of the outer disk that is significantly in excess of
what is expected for a standard planar disk. With enhanced irradiation, the
Esin et al. model can reproduce the optical evolution of A0620-00 in outburst
very well. Though we find that optical observations of GRS 1124-68 also imply
enhanced X-ray heating of the outer disk, the irradiation appears to be a
factor of roughly 3 weaker in this system than in A0620-00. This is surprising,
since GRS 1124-68 has a larger disk. We speculate that enhanced irradiation may
be due to disk warping, and that the degree of warping differs between the two
binaries.
