1. Department of Physics, University of Michigan , Ann Arbor, MI 48109, USA
2. Leinweber Center for Theoretical Physics, University of Michigan , Ann Arbor, MI 48109, USA
3. Department of Physics and Astronomy, University of Pittsburgh , Pittsburgh, PA 15260, USA
4. Pittsburgh Particle Physics, Astrophysics, and Cosmology Center (PITT PACC), University of Pittsburgh , Pittsburgh, PA 15260, USA
5. Department of Physics and Astronomy, Rutgers, The State University of New Jersey , Piscataway, NJ 08854, USA
6. Shanghai Astronomical Observatory , CAS, Shanghai 200030, China
7. Department of Astronomy and Astrophysics, University of California , Santa Cruz, CA 95064, USA
8. Kavli Institute for Particle Astrophysics and Cosmology and Department of Physics, Stanford University , CA 94305, USA
9. Department of Astronomy, Yale University , PO Box 208101, New Haven, CT 06511, USA