R. Pakmor, M. Kromer, S. Taubenberger
The progenitors of Type Ia Supernovae (SNe Ia) are still not known, despite significant progress during the last years in theory and observations. Violent mergers of two carbon--oxygen (CO) white dwarfs (WDs) are one candidate suggested to be responsible for at least a significant fraction of normal SNe Ia. Here, we propose a new, robust, explosion mechanism for violent mergers that works for CO primary WDs with CO as well as helium (He) WD companions. In this mechanism a detonation in the leftover He shell on top of the primary CO WD triggers a second detonation in its core, similar to the well-known double-detonation scenario for helium-accreting CO WDs. However, in contrast to that scenario where a massive He shell is required to form a spontaneous detonation, in the proposed scenario the He detonation is ignited dynamically by a merger of the binary system or instabilities in the accretion stream. Accordingly the required helium-shell mass is significantly smaller, and hence its burning products are unlikely to affect the optical display of the explosion. We show that this scenario has the potential to explain the different brightness distributions, delay times and relative rates of normal and fast declining SNe Ia. Finally, we discuss extensions to our unified merger model needed to obtain a comprehensive picture of the full observed diversity of SNe Ia.
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http://arxiv.org/abs/1302.2913
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