1. Guangxi Key Laboratory for Relativistic Astrophysics, School of Physics Science and Technology, Guangxi University , Nanning 530004 , China
2. Max-Planck-Institut für Kernphysik , P.O. Box 103980, D-69029 Heidelberg , Germany
3. Institute for Theoretical Physics, University of Heidelberg , Philosophenweg 12, D-69120 Heidelberg , Germany
4. School of Astronomy and Space Science, Nanjing University , Nanjing 210093 , China
5. Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University) , Ministry of Education, Nanjing 210023 , China