Origin of the eclipse phase delay in ZTF J0406+0958

Determine the physical origin of the persistent approximately 0.1 orbital-phase delay between the mid-eclipse phase and the principal flux minimum in ZTF J0406+0958.

Background

ZTF J0406+0958 exhibits an eclipse whose midpoint is delayed relative to the main out-of-eclipse flux minimum. The authors argue that the observed modulation is unlikely to arise from the donor star and consider a white-dwarf-related origin, including possible surface spots, but the available photometric and polarimetric data do not establish the cause of the delay.