When will T Coronae Borealis next erupt as a nova? Constraints from recurrence, orbital phase, and accretion-state evolution

ABSTRACT T Coronae Borealis (T CrB) is the nearest symbiotic recurrent nova and is intensively monitored for its next eruption. We combine three constraints on the eruption time: historical recurrence, orbital phase, and recent accretion-state evolution. Conditioning on no eruption by 2026 July 11, the three effective historical intervals give illustrative survival-conditioned probabilities of 30.2 per cent for the rest of 2026 and 56.9 per cent within the following year; these are empirical indicators, not physical prediction probabilities. The four adopted historical eruption phases do not select a unique ignition phase, but form two loose pairs near $\phi \simeq 0.44$ and $\phi \simeq 0.62$, which are used here only as monitoring windows. The 1946 pre-eruption dip is difficult to explain by either a pure accretion-rate decline or standard dust extinction, and may have involved both accretion restructuring and source-dependent obscuration. If the renewed 2026 decline is the true pre-1946 analogue, an eruption around 2026 December remains plausible. Conversely, if post-2024 brightness remains below the 2014–2023 high state, an accretion-deficit estimate gives an earliest lower limit near 2029 May. The data therefore support conditional monitoring windows, not a unique date. These are conditional diagnostic scenarios rather than competing point predictions; the eventual eruption epoch will test their underlying assumptions.