tokens: We thank Wesley Even, Sean M. Couch, Donald Q. Lamb, Ryan Chornock, Ken Chen, Alexandra Kozyreva, and Ragnhild Lunnan for useful discussions and comments. This work was supported in part by the STScI grants AR 12820 and 13276 and the National Science Foundation under grants AST-0909132 and PHY-0822648 for the Physics Frontier Center “Joint Institute for Nuclear Astrophysics” (JINA). E.C. thanks the Enrico Fermi Institute for its support via the Enrico Fermi Fellowship.
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