  Supersoft X-ray sources (SSSs) are characterized by their low effective
temperatures and high X-ray luminosities. The soft X-ray emission can be
explained by hydrogen nuclear burning on the surface of a white dwarf (WD)
accreting at an extremely high rate. A peculiar 67 s periodicity (P67) was
previously discovered in the XMM-Newton light curves of the SSS CAL 83. P67 was
detected in X-ray light curves spanning 9 years, but exhibits variability of
several seconds on time-scales as short as a few hours, and its properties are
remarkably similar to those of dwarf nova oscillations (DNOs). DNOs are short
time-scale modulations often observed in dwarf novae during outburst. DNOs are
explained by the well established low-inertia mag- netic accretor (LIMA) model.
In this paper, we show that P67 and its associated period variability can be
satisfactorily explained by an application of the LIMA model to the more
extreme environment in a SSS (eLIMA), contrary to another recent study at-
tempting to explain P67 and its associated variability in terms of non-radial
g-mode oscillations in the extended envelope of the rapidly accreting white
dwarf in CAL 83. In the eLIMA model, P67 originates in an equatorial belt in
the WD envelope at the boundary with the inner accretion disc, with the belt
weakly coupled to the WD core by a 100 000 G magnetic field. New optical light
curves obtained with the Sutherland High-speed Optical Camera (SHOC) are also
presented, exhibiting quasi-periodic modulations on time-scales of 1000 s,
compatible with the eLIMA framework.
