Discovery of a magnetic white dwarf with unusual short-period variability.

We report the discovery of a magnetic white dwarf which shows periodic variability with P=110 min, color-dependent amplitudes and a transient phase shift in the blue compared to the red lightcurve - a previously unknown type of variability for this type of object. We attribute the variations either to a close ultracool (thus far undetected) companion or, more likely, to magnetic spots with unusual temperature structure.