The Path from the Chinese and Japanese Observations of Supernova 1181 AD, to a Type Iax Supernova, to the Merger of CO and ONe White Dwarfs

Abstract

In 1181 AD, Chinese and Japanese observers reported an unmoving bright `Guest Star' in the constellation Chuanshe, visible for 185 days. 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 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$>$$V_{\rm peak}$$>$$-$1.4, and hence peak absolute magnitude $-$14.5$>$$M_{{\rm 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 one day and longer, critically with no coherent modulations for periods from 0.00046--10 days to strict limits. Fifth, the spectral energy distribution from the far-infrared to the ultraviolet is a nearly-perfect power-law with $F_{\nu}\propto\nu^{0.99\pm0.07}$, observed luminosity 128$\pm$24 L$_{\odot}$, and absolute magnitude $M_{\rm V}$=$+$1.07. I collect my new evidences 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.