The X-ray off-state of the supersoft source CAL 83 and its   interpretation
  We consider simultaneous optical data obtained during the recent X-ray turn-off of CAL83. Combining the optical behaviour with the observed X-ray decay time, we show that a model of cessation of steady nuclear burning is viable if the white dwarf is massive. Our model provides a natural explanation for the subsequent return of the supersoft X-ray emission. 
C. Alcock et al