T CrB from 1943 to 1948. This light curve shows the
B-band (diamonds) and
V-band (circles) magnitudes for an extended period around the 1946 eruption. This extended light curve displays two unique
and still-yet-unexplained phenomena. First, the light curve has a significant and long-duration pre-eruption dip, with the
colors in the dip changing throughout. To get such a dip, either the red giant star would have to be dimmed or the accretion
luminosity would largely have to turn off. A further problem is that if the dip is causally connected to the eruption, then
we must explain why the triggering of the nova event (related to the accumulation of matter on the surface of the white dwarf)
has a dimming (related to either the accretion disk or red giant companion) soon to follow? Second, after T CrB has returned
to quiescence for roughly 50 days, it suddenly rebrightens to eighth magnitude. Such a rise has never been seen in any other
nova event. Is this rebrightening caused by some accretion disk instability or by a further nova event arising from material
falling back on the white dwarf?