1. Department of Physics and Astronomy, Hubei University of Education, Wuhan, China
2. Research Center for Astronomy, Hubei University of Education, Wuhan, China
3. Center for Gravitation and Cosmology, College of Physical Science and Technology, Yangzhou University, Yangzhou, China
4. School of Physics, Peking University, Beijing, China
5. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, China