The B & V light curves for recurrent nova T CrB from 1842–2022, the unique pre- and post-eruption high-states, the complex period changes, and the upcoming eruption in 2025.5 ± 1.3

Abstract

T CrB is one of the most-famous and brightest novae known, and is a recurrent nova with prior eruptions in 1866 and 1946 that peak at V = 2.0. I have constructed light curves spanning 1842–2022 with 213,730 magnitudes, where the B and V magnitudes are fully corrected to the Johnson system. These light curves first reveal a unique complex high-state (with 20× higher accretion rate than the normal low-state) stretching from -10 to +9 years after eruption, punctuated with a deep pre-eruption dip (apparently from dust formation in a slow mass ejection) and a unique enigmatic secondary eruption (with 10 per cent of the energy of the primary eruption), with the light curves identical for the 1866 and 1946 eruptions. Starting in 2015, T CrB entered the high-state, like in 1936, so a third eruption in upcoming years has been widely anticipated. With the pre-1946 light curve as a template, I predict a date of 2025.5 ± 1.3 for the upcoming eruption, with the primary uncertainty arising from a possible lengthening of the pre-eruption high-state. I use the large-amplitude ellipsoidal modulation to track the orbital phase of the binary from 1867–2022. I measure that the orbital period increased abruptly by +0.185 ± 0.056 days across the 1946 eruption, the 1947–2022 years had a steady period decrease of (−8.9 ± 1.6) × 10−6 days-per-day, and the 1867–1946 years had a steady period change consistent with zero, at (+1.75 ± 4.5) × 10−6 days-per-day. These large period changes cannot be explained by any published mechanism.

Symbiotic Star T CrB as an Extreme SU UMa–type Dwarf Nova

“…This could affect the accuracy of our subtraction of the ellipsoidal variability from the light curve. We tested this by changing the parameters of the subtracted orbital variability in accordance with the range of changes noted by Schaefer (2023). We found that the changing orbital variability does not significantly change the smoothed light curve.…”

“…It has been suggested that the last T CrB big active phase is the largest since the 1946 outburst, and the last similar big active phase was seen just before the 1946 outbursts (Munari et al 2016;Luna et al 2020;Schaefer 2023). This may be true regardless of physical interpretation of the brightening and that classical nova eruption could be triggered by a superoutburst.…”

“…Where not all data were in a machinereadable form we digitized the data in the same fashion as discussed by Stanishev et al (2004). Our sample is virtually identical to that presented by Schaefer (2023), except that we limited our analysis to times covered by observations in U, as the amplitude of active phases is best studied in bluest filters. The light curve is presented in Figure 1.…”

“…T CrB experiences active phases, where the UV continuum of the system rises for extended periods of time (e.g., Selvelli et al 1992;Iłkiewicz et al 2016). The most recent active phase was suggested to be connected to the upcoming outburst (e.g., Munari et al 2016;Luna et al 2020;Schaefer 2023). However, Iłkiewicz et al (2016) argued that the active phases are quasiperiodic and are not connected to the classical nova outbursts.…”

The recurrent nova T CrB had prior eruptions observed near December 1787 and October 1217 AD

“…In 2015, with the onset of its unique and characteristic high-state, many workers have realized that T CrB will soon undergo another nova event, estimated for the year 2025.5 ± 1.3. In June 2023, I announced the start of the long-anticipated pre-eruption dip starting in late March, 5 for a possibly-improved eruption date expected for 2024.4 ± 0.3. This bright nova has attracted a variety of evocative storylines.…”