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A hybrid type Ia supernova with an early flash triggered by helium-shell detonation.

Jiang, J-A and Doi, M and Maeda, K and Shigeyama, T and Nomoto, K and Yasuda, N and Jha, SW and Tanaka, M and Morokuma, T and Tominaga, N and Ivezić, Ž and Ruiz-Lapuente, P and Stritzinger, MD and Mazzali, PA and Ashall, C and Mould, J and Baade, D and Suzuki, N and Connolly, AJ and Patat, F and Wang, L and Yoachim, P and Jones, D and Furusawa, H and Miyazaki, S (2017) A hybrid type Ia supernova with an early flash triggered by helium-shell detonation. Nature, 550 (7674). pp. 80-83. ISSN 0028-0836

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Abstract

Type Ia supernovae arise from the thermonuclear explosion of white-dwarf stars that have cores of carbon and oxygen. The uniformity of their light curves makes these supernovae powerful cosmological distance indicators, but there have long been debates about exactly how their explosion is triggered and what kind of companion stars are involved. For example, the recent detection of the early ultraviolet pulse of a peculiar, subluminous type Ia supernova has been claimed as evidence for an interaction between a red-giant or a main-sequence companion and ejecta from a white-dwarf explosion. Here we report observations of a prominent but red optical flash that appears about half a day after the explosion of a type Ia supernova. This supernova shows hybrid features of different supernova subclasses, namely a light curve that is typical of normal-brightness supernovae, but with strong titanium absorption, which is commonly seen in the spectra of subluminous ones. We argue that this early flash does not occur through previously suggested mechanisms such as the companion-ejecta interaction. Instead, our simulations show that it could occur through detonation of a thin helium shell either on a near-Chandrasekhar-mass white dwarf, or on a sub-Chandrasekhar-mass white dwarf merging with a less-massive white dwarf. Our finding provides evidence that one branch of previously proposed explosion models-the helium-ignition branch-does exist in nature, and that such a model may account for the explosions of white dwarfs in a mass range wider than previously supposed.

Item Type: Article
Uncontrolled Keywords: MD Multidisciplinary
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Nature Publishing Group
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Date Deposited: 16 Oct 2017 09:21
Last Modified: 16 Oct 2017 09:21
DOI or Identification number: 10.1038/nature23908
URI: http://researchonline.ljmu.ac.uk/id/eprint/7352

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