1. Center for Astrophysics ∣ Harvard & Smithsonian , 60 Garden St, Cambridge, MA 02138, USA
2. Department of Physics & Astronomy, Johns Hopkins University , 3400 N Charles St, Baltimore, MD 21218, USA
3. Institute for Advanced Study , Einstein Drive, Princeton, NJ 08540, USA
4. Los Alamos National Laboratory , PO Box 1663, Los Alamos, NM 87545, USA
5. Department of Physics and Astronomy, University of Victoria , Victoria, BC V8W 2Y2, Canada
6. Department of Physics & Astronomy, University College London , Gower Street, London WC1E 6BT, UK
7. Department of Physics, University of Warwick , Coventry, CV4 7AL, UK
8. Department of Astronomy and Theoretical Astrophysics Center, University of California , Berkeley, CA 94720, USA
9. Department of Astronomy & Institute for Astrophysical Research, Boston University , 725 Commonwealth Ave., Boston, MA 02215, USA
10. Department of Physics, University of Michigan , 450 Church St, Ann Arbor, MI 48109, USA
11. Department of Physics and Astronomy, University of Sheffield , Sheffield S3 7RH, UK
12. Instituto de Astrofísica de Canarias , E-38205 La Laguna, Tenerife, Spain
13. Isaac Newton Group of Telescopes , Apartado de Correos 321, Santa Cruz de La Palma, E-38700, Spain