1. Department of Physics, Princeton University, Jadwin Hall, Washington Road, New Jersey, 08544, USA
2. Princeton Gravity Initiative, Princeton University, Princeton, New Jersey, 08544, USA
3. Illinois Center for Advanced Studies of the Universe and Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
4. Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Ontario NSL 2Y5, Canada
5. Theoretical Astrophysics, Walter Burke Institute for Theoretical Physics, California Institute of Technology, Pasadena, California 91125, USA
6. Department of Physics and Astronomy, Oberlin College, Oberlin, Ohio 44074, USA
7. Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, New York 14853, USA
8. Department of Physics, Cornell University, Ithaca, New York 14853, USA
9. Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, D-14476 Potsdam, Germany