超新星爆発はどのように進化するのか？(Closest supernova in a decade reveals how exploding stars evolve)

2023-08-29 カリフォルニア大学バークレー校(UCB)

The Pinwheel Galaxy, or Messier 101, on May 21, 2023, four days after the light from the supernova 2023ixf reached Earth.
Steven Bellavia

＜関連情報＞

• https://news.berkeley.edu/2023/08/29/releases-20230828-6895045
• https://arxiv.org/abs/2307.01268
• https://arxiv.org/abs/2306.04721

非対称型II型超新星SN 2023ixfの初期スペクトル偏光測定 Early-time Spectropolarimetry of the Asymmetric Type II Supernova SN 2023ixf

Sergiy S. Vasylyev, Yi Yang, Alexei V. Filippenko, Kishore Patra, Thomas G. Brink, Lifan Wang, Ryan Chornock, Rafaella Margutti, Elinor L. Gates, Adam J. Burgasser, Preethi R. Karpoor, Natalie LeBaron, Emma Softich, Christopher A. Theissen, Eli Wiston, WeiKang Zheng
arXiv  Submitted on 3 Jul 2023
DOI:https://doi.org/10.48550/arXiv.2307.01268

We present six epochs of optical spectropolarimetry of the Type II supernova (SN) 2023ixf ranging from ∼ 2 to 15 days after the explosion. Polarimetry was obtained with the Kast double spectrograph on the Shane 3 m telescope at Lick Observatory, representing the earliest such observations ever captured for an SN. We observe a high continuum polarization pcont≈1 % on days +1.4 and +2.5 before dropping to 0.5 % on day +3.5, persisting at that level up to day +14.5. Remarkably, this change coincides temporally with the disappearance of highly ionized “flash” features. The decrease of the continuum polarization is accompanied by a ∼70^∘ rotation of the polarization position angle (PA) as seen across the continuum. The early evolution of the polarization may indicate different geometric configurations of the electron-scattering atmosphere as seen before and after the disappearance of the emission lines associated with highly-ionized species (e.g., He II, C IV, N III), which are likely produced by elevated mass loss shortly prior to the SN explosion. We interpret the rapid change of polarization and PA from days +2.5 to +4.5 as the time when the SN ejecta emerge from the dense asymmetric circumstellar material (CSM). The temporal evolution of the continuum polarization and the PA is consistent with an aspherical SN explosion that exhibits a distinct geometry compared to the CSM. The rapid follow-up spectropolarimetry of SN 2023ixf during the shock ionization phase reveals an exceptionally asymmetric mass-loss process leading up to the explosion.

メシエ101のSN 2023ixf: 近傍のII型超新星における高密度の近接恒星物質の光イオン化 SN 2023ixf in Messier 101: Photo-ionization of Dense, Close-in Circumstellar Material in a Nearby Type II Supernova

W. V. Jacobson-Galan, L. Dessart, R. Margutti, R. Chornock, R. J. Foley, C. D. Kilpatrick, D. O. Jones, K. Taggart, C. R. Angus, S. Bhattacharjee, L. A. Braff, D. Brethauer, A. J. Burgasser, F. Cao, C. M. Carlile, K. C. Chambers, D. A. Coulter, E. Dominguez-Ruiz, C. B. Dickinson, T. de Boer, A. Gagliano, C. Gall, H. Gao, E. L. Gates, S. Gomez, M. Guolo, M. R. J. Halford, J. Hjorth, M. E. Huber, M. N. Johnson, P. R. Karpoor, T. Laskar, N LeBaron, Z. Li, Y. Lin, S. D. Loch, P. D. Lynam, E. A. Magnier, P. Maloney, D.J. Matthews, M. McDonald, H.-Y. Miao, D. Milisavljevic, Y.-C. Pan, S. Pradyumna, C. L. Ransome, J. M. Rees, A. Rest, C. Rojas-Bravo, N. R. Sandford, L. Sandoval Ascencio, S. Sanjaripour, A. Savino, H. Sears, N. Sharei, S. J. Smartt, E. R. Softich, C. A. Theissen, S. Tinyanont, H. Tohfa, V. A. Villar, Q. Wang, R. J. Wainscoat, A. L. Westerling, E. Wiston, M. A. Wozniak, S. K. Yadavalli, Y. Zenati
arXiv  Submitted on 7 Jun 2023
DOI:https://doi.org/10.48550/arXiv.2306.04721

We present UV/optical observations and models of supernova (SN) 2023ixf, a type II SN located in Messier 101 at 6.9 Mpc. Early-time (“flash”) spectroscopy of SN 2023ixf, obtained primarily at Lick Observatory, reveals emission lines of H I, He I/II, C IV, and N III/IV/V with a narrow core and broad, symmetric wings arising from the photo-ionization of dense, close-in circumstellar material (CSM) located around the progenitor star prior to shock breakout. These electron-scattering broadened line profiles persist for ∼8 days with respect to first light, at which time Doppler broadened features from the fastest SN ejecta form, suggesting a reduction in CSM density at r≳10¹⁵ cm. The early-time light curve of SN2023ixf shows peak absolute magnitudes (e.g., M_u=−18.6 mag, M_g=−18.4 mag) that are ≳2 mag brighter than typical type II supernovae, this photometric boost also being consistent with the shock power supplied from CSM interaction. Comparison of SN 2023ixf to a grid of light curve and multi-epoch spectral models from the non-LTE radiative transfer code CMFGEN and the radiation-hydrodynamics code HERACLES suggests dense, solar-metallicity, CSM confined to r=(0.5−1)×10¹⁵ cm and a progenitor mass-loss rate of M˙=10⁻² M⊙yr⁻¹. For the assumed progenitor wind velocity of vw=50 km s−1, this corresponds to enhanced mass-loss (i.e., “super-wind” phase) during the last ∼3-6 years before explosion.