1. Department of Physics, COMSATS Institute of Information Technology, Park Road, 44000 Islamabad, Pakistan
2. Institut d'Astrophysique de Paris, Sorbonne Universités, UPMC Univ Paris 06 et CNRS, UMR 7095, F-75014 Paris, France
3. Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street, Atlanta, GA 30332, USA