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Permanent URL to this publication: http://dx.doi.org/10.5167/uzh-30866

Botticella, M T; Pastorello, A; Smartt, S J; Meikle, W P S; Benetti, S; Kotak, R; Cappellaro, E; Crockett, R M; Mattila, S; Sereno, M; Patat, F; Tsvetkov, D; Van Loon, J T; Abraham, D; Agnoletto, I; Arbour, R; Benn, C; Di Rico, G; Elias-Rosa, N; Gorshanov, D L; Harutyunyan, A; Hunter, D; Lorenzi, V; Keenan, F P; Maguire, K; Mendez, J; Mobberley, M; Navasardyan, H; Ries, C; Stanishev, V; Taubenberger, S; Trundle, C; Turatto, M; Volkov, I M (2009). SN 2008S: an electron-capture SN from a super-AGB progenitor? Monthly Notices of the Royal Astronomical Society, 398(3):1041-1068.

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Abstract

We present comprehensive photometric and spectroscopic observations of the faint transient SN 2008S discovered in the nearby galaxy NGC 6946. SN 2008S exhibited slow photometric evolution and almost no spectral variability during the first nine months, implying a long photon diffusion time and a high-density circumstellar medium. Its bolometric luminosity (≃1041 erg s−1 at peak) is low with respect to most core-collapse supernovae but is comparable to the faintest Type II-P events. Our quasi-bolometric light curve extends to 300 d and shows a tail phase decay rate consistent with that of 56Co. We propose that this is evidence for an explosion and formation of 56Ni (0.0014 ± 0.0003 M⊙) . Spectra of SN 2008S show intense emission lines of Hα, [Ca ii] doublet and Ca ii near-infrared (NIR) triplet, all without obvious P-Cygni absorption troughs. The large mid-infrared (MIR) flux detected shortly after explosion can be explained by a light echo from pre-existing dust. The late NIR flux excess is plausibly due to a combination of warm newly formed ejecta dust together with shock-heated dust in the circumstellar environment. We reassess the progenitor object detected previously in Spitzer archive images, supplementing this discussion with a model of the MIR spectral energy distribution. This supports the idea of a dusty, optically thick shell around SN 2008S with an inner radius of nearly 90 au and outer radius of 450 au, and an inferred heating source of 3000 K. The luminosity of the central star is L≃ 104.6 L⊙ . All the nearby progenitor dust was likely evaporated in the explosion leaving only the much older dust lying further out in the circumstellar environment. The combination of our long-term multiwavelength monitoring data and the evidence from the progenitor analysis leads us to support the scenario of a weak electron-capture supernova explosion in a super-asymptotic giant branch progenitor star (of initial mass 6–8 M⊙ ) embedded within a thick circumstellar gaseous envelope. We suggest that all of main properties of the electron-capture SN phenomenon are observed in SN 2008S and future observations may allow a definitive answer.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute for Computational Science
DDC:530 Physics
Uncontrolled Keywords:stars: AGB and post-AGB; stars: general; supernovae: general; supernovae: individual: SN 2008S; supernovae: individual: NGC300 OT2008-1; supernovae: individual: M85 OT2006-1
Language:English
Date:September 2009
Deposited On:26 Feb 2010 14:42
Last Modified:27 Nov 2013 21:09
Publisher:Wiley-Blackwell
ISSN:0035-8711
Additional Information:The attached file is a preprint (accepted version) of an article published in Monthly Notices of the Royal Astronomical Society. The definitive version is available at www3.interscience.wiley.com
Publisher DOI:10.1111/j.1365-2966.2009.15082.x
Related URLs:http://arxiv.org/abs/0903.1286

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