On the Formation of the W-shaped O II Lines in Spectra of Type I Superluminous Supernovae
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arXiv
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| Autori principali: | , , , , |
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| Natura: | Preprint |
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2024
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| _version_ | 1866909160439808000 |
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| author | Saito, Sei Tanaka, Masaomi Mazzali, Paolo A. Hachinger, Stephan Hotokezaka, Kenta |
| author_facet | Saito, Sei Tanaka, Masaomi Mazzali, Paolo A. Hachinger, Stephan Hotokezaka, Kenta |
| contents | H-poor superluminous supernovae (SLSNe-I) are characterized by O II lines around 4,000 - 4,500 A in pre-/near-maximum spectra, so-called W-shaped O II lines. As these lines are from relatively high excitation levels, they have been considered a sign of non-thermal processes, which may give a hint of power sources of SLSNe-I. However, the conditions for these lines to appear have not been understood well. In this work, we systematically calculate synthetic spectra to reproduce observed spectra of eight SLSNe-I, parameterizing departure coefficients from the nebular approximation in the SN ejecta (expressed as b_neb). We find that most of the observed spectra can be reproduced well with b_neb ~< 10, which means that no strong departure is necessary for the formation of the W-shaped O II lines. We also show that the appearance of the W-shaped O II lines is sensitive to temperature; only spectra with temperatures T ~ 14,000 - 16,000 K can produce the W-shaped O II lines without large departures. Based on this, we constrain the non-thermal ionization rate near the photosphere. Our results suggest that spectral features of SLSNe-I can give independent constraints on the power source through the non-thermal ionization rates. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2404_03112 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | On the Formation of the W-shaped O II Lines in Spectra of Type I Superluminous Supernovae Saito, Sei Tanaka, Masaomi Mazzali, Paolo A. Hachinger, Stephan Hotokezaka, Kenta High Energy Astrophysical Phenomena Solar and Stellar Astrophysics H-poor superluminous supernovae (SLSNe-I) are characterized by O II lines around 4,000 - 4,500 A in pre-/near-maximum spectra, so-called W-shaped O II lines. As these lines are from relatively high excitation levels, they have been considered a sign of non-thermal processes, which may give a hint of power sources of SLSNe-I. However, the conditions for these lines to appear have not been understood well. In this work, we systematically calculate synthetic spectra to reproduce observed spectra of eight SLSNe-I, parameterizing departure coefficients from the nebular approximation in the SN ejecta (expressed as b_neb). We find that most of the observed spectra can be reproduced well with b_neb ~< 10, which means that no strong departure is necessary for the formation of the W-shaped O II lines. We also show that the appearance of the W-shaped O II lines is sensitive to temperature; only spectra with temperatures T ~ 14,000 - 16,000 K can produce the W-shaped O II lines without large departures. Based on this, we constrain the non-thermal ionization rate near the photosphere. Our results suggest that spectral features of SLSNe-I can give independent constraints on the power source through the non-thermal ionization rates. |
| title | On the Formation of the W-shaped O II Lines in Spectra of Type I Superluminous Supernovae |
| topic | High Energy Astrophysical Phenomena Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2404.03112 |