U Sco fading with enigmatic eclipses

Brad Schaefer reports (priv. comm.) that eclipses are getting broader and deeper, as we have (partially) observed. He writes:

Perfect.  I’ve just constructed the light curve for the last two days, and the eclipses are getting broader and deeper.  I don’t understand this…  We’re getting day-to-day changes, so it is valuable to keep looking.  And the out of eclipse light curve still has that weird assymetry, so look at all nights.

Over the last two days, the X-ray has been brightening, the V-band has been mostly flat, but the UV and IR bands have started a fast fade.

Yuck, this is messy, I have no idea why any of this is happening, and its going on fast.  All of this is the reason to keep taking data.

One would have expected the eclipses to get narrower as the detonated photosphere disperses and becomes a nearly optically transparent expanding shell, and the white dwarf proper reappears and the accretion disk with its bright spot re-forms. But if they’re getting broader then the luminous objects or material must be much wider in the plane of the orbit than before; and because they’re deeper there is less that is escaping the eclipse. This suggests that the shell may have dispersed, at least in the optical, and that a bright accretion disk is forming, one that is everywhere bright rather than primarily at the bright spot where the stream from the donor star impacts the accretion disk – as is the normal case. Effectively, a disk in a dwarf nova outburst.

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