1. Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
2. Center for Interdisciplinary Exploration & Research in Astrophysics (CIERA), Physics & Astronomy, Northwestern University, Evanston, IL 60202, USA
3. Department of Astronomy & Theoretical Astrophysics Center, University of California, Berkeley, CA 94720, USA
4. Department of Physics, University of California, Berkeley, CA 94720, USA
5. Department of Physics and Astronomy, University of New Hampshire, Durham, NH 03824, USA
6. Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA