A new study on a type Iax stellar remnant and its probable association with SN 1181

Abstract

We report observations and modelling of the stellar remnant and presumed double-degenerate merger of Type Iax supernova SN 1181 AD. It is the only known bound stellar SN remnant and the only star with Wolf-Rayet features that is neither a planetary nebula central star nor a massive Pop I progenitor. We model the unique emission-line spectrum with broad, strong O vi and O viii lines as a fast stellar wind and shocked, hot gas. Non-LTE wind modeling indicates a mass-loss rate of ∼ 10 −6 M yr −1 and a terminal velocity of ∼15,000 km s −1 , consistent with earlier results. O viii lines indicate shocked gas temperatures of T 4 MK. We derive a magnetic field upper limit of B < 2.5 MG, below earlier suggestions. The luminosity indicates a remnant mass of 1.2 ± 0.2 M with ejecta mass 0.15 ± 0.05 M . Archival photometry suggests the stellar remnant has dimmed by ∼0.5 magnitudes over 100 years. A low Ne/O < 0.15 argues against a O-Ne white dwarf in the merger. A cold dust shell is only the second detection of dust in a SN Iax and the first of cold dust. Our ejecta mass and kinetic energy estimates of the remnant are consistent with Type Iax extragalactic sources.

Discovery of an Exceptional Optical Nebulosity in the Suspected Galactic SN Iax Remnant Pa 30 Linked to the Historical Guest Star of 1181 CE

“…The electron density sensitive [S II] λ6716/λ6731 line ratio was measured for the brightest filaments and found to range between 1.4 to 0.9 indicating electron densities between 100 − 700 cm −3 with an average ratio around 1.2 (300 cm −3 ) (Osterbrock & Ferland 2006). Although Ritter et al (2021) do not quote electron densities measured from their GTC/OSIRIS observed [S II] line ratios, Lykou et al (2022) states the average [S II] derived density value from those data was 120 cm −3 , which is a bit lower than the average we found. Also, in the few cases where there was a significant brightness difference between the ends of a filament, the filaments' brightest portion displayed the lowest velocity, suggesting the densest portions of these filaments lies closer in to the remnant's center.…”

“…The remnant's hot central star, called J005311 based on its J2000 coordinates (α=00 h 53 m 11.2 s , δ=+67 • 30 2.4 ), has been proposed to be either a high mass white dwarf (WD), a super-Chandrasekhar-mass WD, or the result of a double degenerate merger which resulted in a SN Iax explosion (Gvaramadze et al 2019;Kashiyama et al 2019;Oskinova et al 2020;Lykou et al 2022). While the convergence point of the remnant's filaments lies very close to Pa 30's hot central star, a few of the brighter filaments do not appear in perfect alignment with the star's current position.…”

“…A newly recognized Galactic nebula, Pa 30 (G123.1+4.6), located not far from 3C 58 and actually nearer the spot cited by Chinese and Japanese observers, has recently been identified as the likely true remnant of SN 1181 (Ritter et al 2021;Lykou et al 2022;Schaefer 2022). Initially identified as a possible planetary nebula (Patchick candidate number 30), it was subsequently found associated with a very hot star (∼210,000 K) with an astounding 16,000 km s −1 velocity wind (Gvaramadze et al 2019;Garnavich et al 2020).…”

“…Initially identified as a possible planetary nebula (Patchick candidate number 30), it was subsequently found associated with a very hot star (∼210,000 K) with an astounding 16,000 km s −1 velocity wind (Gvaramadze et al 2019;Garnavich et al 2020). A young SNR with a hot surviving compact object suggests that it may be the remnant of a doubledegenerate merger leading to a subtype Ia SN known as a SN Iax (Gvaramadze et al 2019;Kashiyama et al 2019;Oskinova et al 2020;Ritter et al 2021;Lykou et al 2022).…”

“…Deep [O III] λ5007 line emission images revealed a faint and diffuse emission nebula (Kronberger et al 2014;Ritter et al 2021) while spectra show [S II] λλ6716, 6731 emission with an expansion velocity ∼1100 km s −1 (Ritter et al 2021). Because of its known [S II] emission and a high estimated interstellar extinction (E(B − V ) 0.85; Ritter et al 2021;Lykou et al 2022), we thought it worthwhile to explore the optical structure of this young and nearby suspected SN Iax remnant through red [S II] images.…”