The connection between accretion disk brightness and the white dwarf (WD) reaching the trigger threshold is too weak to be usable, at least for fast timescales. The steady optical light is dominated by the middle of the accretion disk, while the flickering is dominated by closer-in regions of the disk. The inward motions of gas at these disk-radii have timescales of days to months. With ordinary viscocity, a particularly dense clump of mass inside the disk will be smeared out as part of it goes to lower WD-distances, so that its arrival time on the WD will also be smeared out over days-to-months. So we do not expect any sudden dumping of gas landing on the WD. So the increase of the accretion rate onto the WD will be smeared and delayed from seeing any optical brightening in the accretion disk. The accretion rate onto the WD has little immediate connection to the temperature deep within the WD (at the base of the accumulated fresh hydrogen fuel). The reason is that the thermal conduction timescale from the surface to the interior is long. With this diffusion of heat, any thermal pulses from accretion get smeared out further. So there is no ready connection from a brightening in the middle-disk to the temperature at the base of the layer of accumulated fuel. These comments apply for relatively fast variations in the accretion brightness.
For prolonged high states (longer than the various diffusion timescales), the eruption would indeed be more likely to occur during the high state. To use an analogy, a bathtub is more likely to overflow when being filled with the faucet turned on high than when being filled with a leaky dripping faucet. The time when the last gram arrives to push the WD over the trigger threshold for the runaway could happen at either high or low accretion rate. With more mass arriving at the WD during high states (?), the nova eruption is more likely during a high state of accretion.
With this, we can see why T CrB erupts after ten years of being in its pre-eruption high state. Uurgghh, but then why do the eruptions actually wait for a year after the end of that high state (in what is labeled as the pre-eruption dip)? So the last eruption actually happened when T CrB was in its low state. And why did the high state start and stop? And why did the start and stop times in 2015 and 2024 match the start and stop times in the previous eruption (1935 and 1945)? Such matching shows that the high states in T CrB are not random, but involve a nearly-deterministic scenario that we have not yet know or understand.
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