1. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China
2. Department of Astronomy, School of Physics, Peking University, Beijing 100871, China
3. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
4. Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA
5. Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV 26505, USA
6. Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154, USA