Spectropolarimetry of Type II supernovae: II. Intrinsic supernova polarization and its relation to photometric and spectroscopic properties

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Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2024-01-01
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Mcode
Degree programme
Language
en
Pages
Series
Astronomy and Astrophysics, Volume 681
Abstract
The explosion processes of supernovae (SNe) are imprinted in their explosion geometries. The recent discovery of several highly aspherical core-collapse SNe is significant, and studying these is regarded as being crucial in order to understand the underlying explosion mechanism. Here, we study the intrinsic polarization of 15 hydrogen-rich core-collapse SNe and explore the relation between polarization and the photometric and spectroscopic properties of these objects. Our sample shows diverse properties of the continuum polarization. Most SNe show a low degree of polarization at early phases but a sudden rise to ∼1% at certain points during the photospheric phase followed by a slow decline during the tail phase, with a constant polarization angle. The variation in the timing of peak polarization values implies diversity in the explosion geometry: some SNe have aspherical structures only in their helium cores, while in other SNe such structures reach out to a significant part of the outer hydrogen envelope with a common axis from the helium core to the hydrogen envelope. Other SNe show high polarization from early phases and a change in polarization angle around the middle of the photospheric phase. This implies that the ejecta are significantly aspherical out to the outermost layer and have multi-directional aspherical structures. Exceptionally, the Type IIL SN 2017ahn shows low polarization at both the photospheric and tail phases. Our results show that the timing of the polarization rise in Type IIP SNe is likely correlated with their brightness, velocity, and the amount of radioactive Ni produced: brighter SNe with faster ejecta velocity and a larger 56Ni mass have more extended aspherical explosion geometries. In particular, there is a clear correlation between the timing of the polarization rise and the explosion energy; that is, the explosion asphericity is proportional to the explosion energy. This implies that the development of a global aspherical structure, such as a jet, might be the key for the realisation of an energetic SN in the mechanism of SN explosions.
Description
Funding Information: We thank Keiichi Maeda, Masaomi Tanaka and Giuliano Pignata for useful discussions. T.N. was supported by a Japan Society for the Promotion of Science (JSPS) Overseas Research Fellowship and was funded by the Academy of Finland project 328898. H.K. was funded by the Academy of Finland projects 324504 and 328898. S.M. was funded by the Academy of Finland project 350458. This research has made use of NASA's Astrophysics Data System Bibliographic Services. Funding Information: We thank Keiichi Maeda, Masaomi Tanaka and Giuliano Pignata for useful discussions. T.N. was supported by a Japan Society for the Promotion of Science (JSPS) Overseas Research Fellowship and was funded by the Academy of Finland project 328898. H.K. was funded by the Academy of Finland projects 324504 and 328898. S.M. was funded by the Academy of Finland project 350458. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. Publisher Copyright: © 2024 The Authors.
Keywords
Supernovae: general, Techniques: polarimetric
Other note
Citation
Nagao, T, Patat, F, Cikota, A, Baade, D, Mattila, S, Kotak, R, Kuncarayakti, H, Bulla, M & Ayala, B 2024, ' Spectropolarimetry of Type II supernovae : II. Intrinsic supernova polarization and its relation to photometric and spectroscopic properties ', Astronomy and Astrophysics, vol. 681, A11 . https://doi.org/10.1051/0004-6361/202346715