[1] Eberhard Karls Univ Tubingen, Theoret Astrophys, D-72076 Tubingen, Germany
[2] Bulgarian Acad Sci, INRNE, Sofia 1784, Bulgaria
[3] Koc Univ, Dept Phys, Rumelifeneri Yolu, TR-34450 Sariyer, Istanbul, Turkiye
[4] Albert Einstein Inst, Max Planck Inst Grav Phys, D-14476 Potsdam, Germany
[5] Univ Nottingham, Nottingham Ctr Grav, Univ Pk, Nottingham NG7 2RD, England
[6] Univ Nottingham, Sch Math Sci, Univ Pk, Nottingham NG7 2RD, England
[7] Univ Nottingham, Sch Phys & Astron, Univ Pk, Nottingham NG7 2RD, England
[8] Univ Tubingen, IAAT, Theoret Astrophys, D-72076 Tubingen, Germany
[9] Sofia Univ, Fac Phys, Dept Theoret Phys, Sofia 1164, Bulgaria
[10] Bulgarian Acad Sci, Inst Math & Informat, Acad Georgi Bonchev St 8, Sofia 1113, Bulgaria