1. Janusz Gil Institute of Astronomy, University of Zielona Góra, 65-516 Zielona Góra, Poland
2. Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA
3. Center for Gravitational Physics and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV 26505, USA
4. Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester M13 9PL, UK
5. Inter-University Centre for Astronomy and Astrophysics, Pune 411007, India