  The 2006 outburst of GK Perseii differed significantly at optical and
ultraviolet wavelengths from typical outbursts of this object. We present
multi-wavelength (X-ray, UV and optical) Swift and AAVSO data, giving
unprecedented broad-band coverage of the outburst, allowing us to follow the
evolution of the longer-than-normal 2006 outburst across these wavelengths. In
the optical and UV we see a triple-peaked morphology with maximum brightness
~1.5 magnitudes lower than in previous years. In contrast, the peak hard X-ray
flux is the same as in previous outbursts. We resolve this dichotomy by
demonstrating that the hard X-ray flux only accounts for a small fraction of
the total energy liberated during accretion, and interpret the optical/UV
outburst profile as arising from a series of heating and cooling waves
traversing the disc, caused by its variable density profile.
