Supernova SN 1181 & Pa 30 Remnant
- Supernova SN 1181 is a historically recorded Galactic transient identified as a sub-luminous Type Iax event from a double-degenerate white dwarf merger.
- Its remnant, Pa 30, features an ultra-hot, hydrogen- and helium-deficient central star and a filamentary nebula, serving as a unique laboratory for merger dynamics.
- Multiwavelength studies of SN 1181 reveal detailed ejecta kinematics, shock interactions, and dust characteristics that refine models of Type Iax supernova explosions.
Supernova SN 1181 is a historically recorded Galactic transient observed in AD 1181, now conclusively identified as a sub-luminous Type Iax supernova event resulting from a double-degenerate merger of white dwarfs. Its remnant, Pa 30 (centering on the O-rich Wolf–Rayet star IRAS 00500+6713 / J005311, also “Parker’s star”), uniquely enables direct paper of both the surviving stellar remnant and the ejecta, providing a benchmark for white dwarf merger physics and supernova diversity.
1. Historical Observations and Identification
Multiple independent records detail the guest star of AD 1181, including Chinese, Japanese, and, newly, Arabic sources (Fischer et al., 4 Sep 2025). These describe a stationary transient in Cassiopeia (al-Kaff al-Khaḍīb), visible for ca. 185 days, peaking at a visual magnitude between 0 and −1.4 (Schaefer, 2023, Fischer et al., 4 Sep 2025). This excludes novae or comets, indicating a supernova event. The new Arabic poem from Cairo, contemporaneous to 1181, identifies the star in Cassiopeia, brighter than α Cas (2.25 mag), closely matching East Asian positional and brightness constraints (Fischer et al., 4 Sep 2025).
Table 1: SN 1181 Historical Data
| Culture | Dates (AD 1181) | Sky Region | Max Brightness |
|---|---|---|---|
| Chinese | Aug–Feb | Chuanshe/Cassiopeia | 0.0 > V > −1.4 |
| Japanese | Aug–Feb | Chuanshe/Cassiopeia | Comparable to Saturn |
| Arabic | Dec–May | al-Kaff al-Khaḍīb (Cassiopeia) | > 2.25 mag (α Cas) |
These records, combined with modern astrometry (Gaia DR3 d ≈ 2.3–2.5 kpc) and extinction (E(B–V) ≈ 0.84), yield a peak absolute magnitude −14.5 > M_V,peak > −16.0 (Schaefer, 2023), confirming it as a sub-luminous supernova.
2. Remnant Association: Pa 30 and “Parker’s Star”
The identification of Pa 30 as the SN 1181 remnant was established by multi-wavelength investigations (Ritter et al., 2021). The SNR is centered on an exceptionally hot hydrogen- and helium-deficient star, exhibiting O-dominated Wolf–Rayet–like spectra. Earlier candidates (e.g., 3C58) are now excluded due to age (>3000 yr) and location inconsistencies (Ritter et al., 2021, Fischer et al., 4 Sep 2025).
Key parameters:
- Central star: IRAS 00500+6713/J005311, T_eff ≈ 200,000–260,000 K, rapid wind v_terminal ≈ 15,000–16,000 km/s (Lykou et al., 2022, Fesen et al., 2023, Cunningham et al., 14 Oct 2024)
- Nebula diameter: θ ≈ 170″, d ≈ 2.3 kpc, physical size ≈ 1.9 pc
- Remnant age: t_k ≈ d/(2 v_exp) ≈ 990{+280}_{−220} years (Ritter et al., 2021)
- Ejecta velocity: v_exp ≈ 1100 km/s, consistent with expansion over ∼840–1150 yr (Schaefer, 2023, Cunningham et al., 14 Oct 2024)
The nebular and stellar spectral and kinematic properties, coupled with position, confirm Pa 30’s association with SN 1181.
3. Physical Properties: Structure, Composition, and Kinematics
Pa 30’s nebula displays a unique filamentary, radially symmetric structure, with dozens of filaments converging on its hot central star (Fesen et al., 2023, Cunningham et al., 14 Oct 2024). Electron density diagnostics via [S II] λ6716/λ6731 yield n_e ≈ 100–700 cm⁻³ (Fesen et al., 2023). No Hα emission is detected (I[6716/Hα] > 5), with faint [Ar III] λ7136, indicating H-poor, S, Ar-rich composition. Infrared imaging (WISE, Spitzer) reveals a thick shell and a sharp inner edge corresponding to a dust-rich cavity, with dust mass ≈ 8 × 10⁻³ M_☉ at T ≈ 60 K (Lykou et al., 2022, Cunningham et al., 14 Oct 2024).
Integral field spectroscopy (KCWI) enables 3D mapping of ejecta velocities and positions ([S II] doublet). The ejecta expansion is nearly ballistic (v = k · r / τ, k ≈ 0.97), with minimal deceleration since explosion (Cunningham et al., 14 Oct 2024). A pronounced flux asymmetry is observed: redshifted filaments are ∼40% brighter than blueshifted, suggesting explosion asymmetry or uneven ejecta distribution.
Table 2: Pa 30 Remnant Physical Parameters
| Quantity | Value (approximate) |
|---|---|
| Age | 990{+280}_{−220} yr |
| Ejecta velocity | ≈ 1100 km/s |
| Wind speed (central star) | ≈ 16,000 km/s |
| Ejecta mass | 0.15 ± 0.05 M_☉ |
| Dust mass (cold shell) | ≈ 8e-3 M_☉ |
| Electron density | 100–700 cm⁻³ |
4. Double-Degenerate Merger and Type Iax Supernova Mechanism
The spectral and morphological evidence favors a double-degenerate (CO+ONe WD) merger for SN 1181, leading to a subluminous Type Iax explosion (Ritter et al., 2021, Lykou et al., 2022, Ko et al., 2023). The merger triggers a weak thermonuclear explosion: only part of the system is unbound, ejecting ∼0.1–0.5 M_☉ at ∼1100 km/s, while the remnant star survives as an O-rich-helium-poor compact object. The peculiar abundances—H and He deficiency, O/C dominance, Ne/O < 0.15—exclude standard core-collapse and favor CO-rich merger products (Lykou et al., 2022).
Late-time evolution is modulated by delayed wind onset (∼810–828 yr post-explosion, after A.D. 1990), interpreted as resulting from Kelvin–Helmholtz contraction and carbon-burning in the ONe core (Ko et al., 2023). The inner X-ray nebula thus forms as the fast wind collides with fallback ejecta, and the outer nebula at the expanding SNR–ISM interface.
Key formula for kinematic age:
with in radians and from Gaia astrometry.
5. Multiwavelength Observations: X-ray, Infrared, Radio
X-ray imaging (XMM–Newton, Chandra) resolves two nebular components (Ko et al., 2023):
- Inner nebula: wind termination shock, enriched in carbon-burning ashes, angular radius ∼0.77–1.6″, T_shock ≈ 4 MK, metal-rich, low H.
- Outer nebula: shocked SN ejecta and ISM, angular extent ≈ 131″, composition closer to solar.
Infrared SEDs (WISE, AKARI, IRAS) fit cold dust at T ≈ 60 K (Lykou et al., 2022); the shell marks a shock boundary correlating with optical filament inner edges.
Radio emission models predict synchrotron fluxes: outer SNR shock (0.1–10 mJy at 0.01–1 GHz), inner termination shock (0.01–0.1 mJy at 1–10 GHz) (Ko et al., 23 Jan 2024). Archival searches (VLASS, NVSS, CGPS) yield non-detections; higher-sensitivity, high-frequency, high-resolution observations are strongly encouraged to resolve the termination shock and assess wind–ejecta interaction dynamics.
6. Implications and Broader Significance
The SN 1181/Pa 30 association establishes the first unambiguous identification of a Type Iax supernova in the Galaxy (Ritter et al., 2021, Schaefer, 2023). Observational access to both the stellar remnant and young ejecta provides a laboratory for testing merger dynamics, thermonuclear explosion mechanisms, wind evolution, and SNR chemistry. Empirical constraints (t_k, M_ej, v_exp, chemical stratification) support models of failed detonations/sub-Chandrasekhar mass explosions with persistent post-SN winds.
Historically, the multi-cultural records (Chinese, Japanese, Arabic) enable precise cross-dating and localization, validating the merger scenario and challenging earlier associations (3C58) (Fischer et al., 4 Sep 2025). Improved dating—down to months—advances reconstructive modeling for remnant ages and progenitor properties.
Future observational priorities include high-resolution integral field mapping (optical, infrared, radio), detailed dust characterization, long-term photometric monitoring of the remnant star, and expansion tracking to further constrain the explosion asymmetry and wind–ejecta interactions.
7. Comparative Perspective and Theoretical Importance
Pa 30 represents a benchmark for Type Iax SN remnants with surviving stars. Comparative analysis with extragalactic Type Iax events affirms subluminous, low-energy explosions, small ejecta mass, and unique post-SN dust formation (Lykou et al., 2022). Absence of He and H in the ejecta and wind corroborates the double-degenerate merger channel as a key pathway for these supernovae (Ko et al., 2023).
The observed nebular and wind structure demands refined models of white dwarf mergers and failed SN explosions, integrating effects of delayed, chemically enriched winds, wind–shell interactions, and asymmetric ejecta (Cunningham et al., 14 Oct 2024). The presence of a ballistic, asymmetric ejecta distribution and central cavity are of particular interest for simulation and hydrodynamic modeling.
Pa 30/SN 1181 thus provides an unprecedented opportunity to empirically anchor the Galactic occurrence, physics, and post-explosion evolution of double-degenerate Type Iax supernovae.