A post not about the next eruption, but about two previous ones in 1787 and 1217!
A JHA pre-print by Prof Brad Schaefer The recurrent nova T CrB had prior eruptions observed near December 1787 and October 1217 AD appears on ArXiv today: https://arxiv.org/abs/2308.13668
He comments “T CrB has four observed eruptions in the years 1217.8, 1787.9, 1866.4, and
1946.1, plus one more expected upcoming in 2024.4±0.3. The recurrence
timescales are 7×81.4, 78.5, 79.7, and likely 78.3±0.3 years. With 9 eruptions
from 1217.8 to 1946.1, the average recurrence timescale is 80.9 years. I expect
additional eruptions within a year or two of 1706, 1625, 1544, 1462, 1381, 1299,
1137, 1055, 974, 892, 811, 730, 648, 567, 485, 404, 323, 241, 160, and 78 AD. ”
Abstract:
The famous recurrent nova (RN) T Coronae Borealis (T CrB) has had observed eruptions peaking at a visual magnitude of 2.0 in the years 1866 and 1946, while a third eruption is now expected for the year 2024.4+-0.3. Each RN has very similar light curves of eruptions that come with a fairly even-spacing in time, for which T CrB has a recurrence timescale near 80 years. So it is reasonable to look backwards in time for prior eruptions, around 1786, and so on back. I have investigated two long-lost suggestions that T CrB was seen in eruption in the years 1217 and 1787. (1) In a catalog published in 1789, the Reverend Francis Wollaston reports an astrometric position for a star that is exactly on top of T CrB. From his letters, these observations were made on at least four occassions with both a large and small telescope, within a few days before 1787 December 28. Wollaston’s limiting magnitude for his astrometry is near 7.8 mag, so T CrB would have to have been in eruption. With other transients strongly rejected, the only way that Wollaston could get the coordinates was to have measured the coordinates of T CrB itself during an eruption. (2) The 1217 event has an eyewitness report written by Abbott Burchard of Upsberg as a fast-rising stellar point-source (“stella”) in Corona Borealis that “shone with great light”, lasted for “many days”, and was ascribed as being a “wonderful sign”. This event cannot be a report of a comet, because Burchard used the term for a star (“stella”) and not for a comet, and because Burchard had the omen being very positive, with such being impossible for comets that are universally the worst of omens. The reported event is just as expected for a prior eruption of T CrB, and all other possibilities are strongly rejected, so the case for the 1217 eruption of T CrB is strong.
