2023MNRAS.523.3885S

In 1181 AD, Chinese and Japanese observers reported an unmoving bright 'Guest Star' in the constellation Chuanshe, visible for 185 d. In 2013, D. Patchick discovered what turned out to be a unique nebula surrounding a unique star, with the structure named 'Pa 30', while subsequent workers made connections to mergers of white dwarfs, to the supernova subclass of low-luminosity Type Iax, and to the 1181 transient. Here, I provide a wide range of new observational pieces of evidence: First, detailed analysis of the original Chinese and Japanese reports places the 'Guest Star' of 1181 into a small region with the only interesting source being Pa 30. Second, the ancient records confidently place the peak magnitude as 0.0 > V_peak > -1.4, and hence peak absolute magnitude -14.5 >M_V, peak_>-16.0 mag. Third, the Pa 30 central star is fading from B = 14.9 in 1889, to B = 16.20 in 1950, to B = 16.58 in 2022. Fourth, recent light curves show typical variability with full amplitude of 0.24 mag on time-scales of 1 d and longer, critically with no coherent modulations for periods from 0.00046-10 d to strict limits. Fifth, the spectral energy distribution from the far-infrared to the ultraviolet is a nearly perfect power law with F_ν ∝ ν^0.99 ± 0.07^, observed luminosity 128 ± 24 L_⊙, and absolute magnitude M_V = +1.07. I collect my new pieces of evidence with literature results to make a confident case to connect the East-Asian observations to a supernova, then to Pa 30, then to a low-luminosity Type Iax SN, then to the only possible explosion mechanism as a merger between CO and ONe white dwarfs.