Jiang, Ji-An; Doi, Mamoru; Maeda, Keiichi; Shigeyama, Toshikazu; Nomoto, Ken’Ichi; Yasuda, Naoki; Jha, Saurabh W.; Tanaka, Masaomi; Morokuma, Tomoki; Tominaga, Nozomu; Ivezić, Željko; Ruiz-Lapuente, Pilar; Stritzinger, Maximilian D.; Mazzali, Paolo A.; Ashall, Christopher; Mould, Jeremy; Baade, Dietrich; Suzuki, Nao; Connolly, Andrew J.; Patat, Ferdinando; Wang, Lifan; Yoachim, Peter; Jones, D.; Furusawa, Hisanori; Miyazaki, Satoshi
Bibliographical reference
Nature, Volume 550, Issue 7674, pp. 80-83 (2017).
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2017
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Citations
112
Refereed citations
103
Description
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.
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